Try opening relative path files from internal storage.

I'm not falling back to external storage because the application should be
aware of whether external storage is available and choose whether or not to
use it.

src/file/SDL_rwops.c

@@ -429,13 +429,28 @@ SDL_RWFromFile(const char *file, const char *mode)
 #if defined(ANDROID)
 #ifdef HAVE_STDIO_H
     /* Try to open the file on the filesystem first */
-    {
+    if (*file == '/') {
         FILE *fp = fopen(file, mode);
         if (fp) {
             return SDL_RWFromFP(fp, 1);
         }
+    } else {
+        /* Try opening it from internal storage if it's a relative path */
+        char *path;
+        FILE *fp;
+
+        path = SDL_stack_alloc(char, PATH_MAX);
+        if (path) {
+            SDL_snprintf(path, PATH_MAX, "%s/%s",
+                         SDL_AndroidGetInternalStoragePath(), file);
+            fp = fopen(path, mode);
+            SDL_stack_free(path);
+            if (fp) {
+                return SDL_RWFromFP(fp, 1);
+            }
+        }
     }
-#endif
+#endif /* HAVE_STDIO_H */
 
     /* Try to open the file from the asset system */
     rwops = SDL_AllocRW();