fix various problems, thanks CppCheck :) (#1005)

* explained a bit more the core_window_letterbox example

* fixed a few 'ups' moments that could lead to mild head pain and time loss

src/models.c

@@ -929,12 +929,16 @@ ModelAnimation *LoadModelAnimations(const char *filename, int *animCount)
     {
         TraceLog(LOG_ERROR, "Magic Number \"%s\"does not match.", iqm.magic);
         fclose(iqmFile);
+
+        return NULL;
     }
 
     if (iqm.version != IQM_VERSION)
     {
         TraceLog(LOG_ERROR, "IQM version %i is incorrect.", iqm.version);
         fclose(iqmFile);
+        
+        return NULL;
     }
 
     // Get bones data

src/physac.h

@@ -842,9 +842,17 @@ PHYSACDEF void DestroyPhysicsBody(PhysicsBody body)
             }
         }
 
-        #if defined(PHYSAC_DEBUG)
-        if (index == -1) printf("[PHYSAC] cannot find body id %i in pointers array\n", id);
-        #endif
+        
+        if (index == -1){
+
+            #if defined(PHYSAC_DEBUG)
+                printf("[PHYSAC] cannot find body id %i in pointers array\n", id);
+            #endif
+
+        // prevent access to index -1
+        return;
+        } 
+        
 
         // Free body allocated memory
         PHYSAC_FREE(body);
@@ -1249,9 +1257,16 @@ static void DestroyPhysicsManifold(PhysicsManifold manifold)
             }
         }
 
-        #if defined(PHYSAC_DEBUG)
-            if (index == -1) printf("[PHYSAC] cannot find manifold id %i in pointers array\n", id);
-        #endif
+
+        if (index == -1) {
+            #if defined(PHYSAC_DEBUG)
+                printf("[PHYSAC] cannot find manifold id %i in pointers array\n", id);
+            #endif
+
+            //prevent access to index -1
+            return;
+        } 
+        
 
         // Free manifold allocated memory
         PHYSAC_FREE(manifold);

src/raudio.c

@@ -592,13 +592,14 @@ void SetMasterVolume(float volume)
 AudioBuffer *InitAudioBuffer(ma_format format, ma_uint32 channels, ma_uint32 sampleRate, ma_uint32 bufferSizeInFrames, int usage)
 {
     AudioBuffer *audioBuffer = (AudioBuffer *)RL_CALLOC(1, sizeof(AudioBuffer));
-    audioBuffer->buffer = RL_CALLOC(bufferSizeInFrames*channels*ma_get_bytes_per_sample(format), 1);
 
     if (audioBuffer == NULL)
     {
         TraceLog(LOG_ERROR, "InitAudioBuffer() : Failed to allocate memory for audio buffer");
         return NULL;
     }
+    
+    audioBuffer->buffer = RL_CALLOC(bufferSizeInFrames*channels*ma_get_bytes_per_sample(format), 1);
 
     // Audio data runs through a format converter
     ma_pcm_converter_config dspConfig;

src/rlgl.h

@@ -1887,6 +1887,13 @@ unsigned int rlLoadTexture(void *data, int width, int height, int format, int mi
 #endif
 #endif      // GRAPHICS_API_OPENGL_11
 
+    if( data == NULL ){
+        //ups!
+        TraceLog(LOG_WARNING, "Got asked to load texture from a NULL pointer!");
+
+        return id;
+    }
+
     glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 
     glGenTextures(1, &id);              // Generate texture id

src/shapes.c

@@ -1524,7 +1524,7 @@ static float EaseCubicInOut(float t, float b, float c, float d)
 // Get texture to draw shapes (RAII)
 static Texture2D GetShapesTexture(void)
 {
-    if (texShapes.id <= 0)
+     if (texShapes.id == 0) //this variable is an unsigned int, will never be negative
     {
 #if defined(SUPPORT_FONT_TEXTURE)
         texShapes = GetFontDefault().texture;           // Use font texture white character

src/text.c

@@ -1394,7 +1394,7 @@ char *TextToUtf8(int *codepoints, int length)
     }
     
     // Resize memory to text length + string NULL terminator
-    realloc(text, size + 1);
+    text = realloc(text, size + 1);
     
     return text;
 }

src/textures.c

@@ -662,7 +662,7 @@ Vector4 *GetImageDataNormalized(Image image)
                     pixels[i].w = 1.0f;
 
                     k += 3;
-                }
+                } break;
                 case UNCOMPRESSED_R32G32B32A32:
                 {
                     pixels[i].x = ((float *)image.data)[k];