RISC OS: Ensure core windows are fully initialised.

frontends/riscos/cookies.c

@@ -377,7 +377,7 @@ static nserror ro_cookie_init(void)
 		return NSERROR_OK;
 	}
 
-	ncwin = malloc(sizeof(struct ro_cookie_window));
+	ncwin = calloc(1, sizeof(*ncwin));
 	if (ncwin == NULL) {
 		return NSERROR_NOMEM;
 	}

frontends/riscos/global_history.c

@@ -405,7 +405,7 @@ static nserror ro_global_history_init(void)
 		return NSERROR_OK;
 	}
 
-	ncwin = malloc(sizeof(struct ro_global_history_window));
+	ncwin = calloc(1, sizeof(*ncwin));
 	if (ncwin == NULL) {
 		return NSERROR_NOMEM;
 	}

frontends/riscos/hotlist.c

@@ -466,7 +466,7 @@ static nserror ro_hotlist_init(void)
 		return NSERROR_OK;
 	}
 
-	ncwin = malloc(sizeof(struct ro_hotlist_window));
+	ncwin = calloc(1, sizeof(*ncwin));
 	if (ncwin == NULL) {
 		return NSERROR_NOMEM;
 	}

frontends/riscos/local_history.c

@@ -299,7 +299,7 @@ ro_local_history_init(struct browser_window *bw,
 		return res;
 	}
 
-	ncwin = malloc(sizeof(struct ro_local_history_window));
+	ncwin = calloc(1, sizeof(*ncwin));
 	if (ncwin == NULL) {
 		return NSERROR_NOMEM;
 	}