validate-icon: Add file limit of 4MB

Images shouldn't be to big in size. 4MBs is more then enough for all
cases.

src/validate-icon.c

@@ -39,6 +39,7 @@
 #define MAX_ICON_SIZE 512
 #define MAX_SVG_ICON_SIZE 4096
 #define BUFFER_SIZE 4096
+#define MAX_FILE_SIZE 4194304 /* Max file size of 4MB */
 
 static int
 validate_icon (int input_fd)
@@ -72,6 +73,12 @@ validate_icon (int input_fd)
       return 1;
     }
 
+  if (g_bytes_get_size (bytes) > MAX_FILE_SIZE)
+    {
+      g_printerr ("Image is bigger then the allowed size\n");
+      return 1;
+    }
+
   loader = gdk_pixbuf_loader_new ();
 
   if (!gdk_pixbuf_loader_write_bytes (loader, bytes, &error) ||