Revert "Removed save GPR code in read_sector"

This reverts commit c797223699c06722890183248ef059ce3f2c0de7.

bootsect/disk.inc

@@ -13,6 +13,13 @@ read_sector:
 ; OUT:
 ; Carry if error
 
+push eax
+push ebx
+push ecx
+push edx
+push esi
+push edi
+
 push es
 pop word [.target_segment]
 mov word [.target_offset], bx
@@ -27,6 +34,13 @@ clc										; Clear carry for int 0x13 because some BIOSes may not clear it on
 int 0x13								; Call int 0x13
 
 .done:
+
+pop edi
+pop esi
+pop edx
+pop ecx
+pop ebx
+pop eax
 ret										; Exit routine
 
 align 4