Silence some Coverity errors

cheevos/cheevos.c

@@ -1028,11 +1028,11 @@ static int cheevos_parse_expression(cheevos_expr_t *expr, const char* mem)
    cheevos_term_t *terms  = NULL;
    char       *end        = NULL;
 
-   if (expr)
-   {
-      expr->count         = 1;
-      expr->compare_count = 1;
-   }
+   if (!expr)
+      return -1;
+
+   expr->count            = 1;
+   expr->compare_count    = 1;
 
    for (aux = mem;; aux++)
    {

libretro-common/formats/png/rpng_encode.c

@@ -354,7 +354,8 @@ static bool rpng_save_image(const char *path,
       GOTO_END_ERROR();
 
 end:
-   filestream_close(file);
+   if (file)
+      filestream_close(file);
    free(encode_buf);
    free(deflate_buf);
    free(rgba_line);

libretro-common/vfs/vfs_implementation.c

@@ -251,12 +251,9 @@ libretro_vfs_implementation_file *retro_vfs_file_open_impl(const char *path, uns
 
    if ((stream->hints & RFILE_HINT_UNBUFFERED) == 0)
    {
-      if (!mode_str)
-         goto error;
+      FILE   *fp = fopen_utf8(path, mode_str);
 
-      stream->fp = fopen_utf8(path, mode_str);
-
-      if (!stream->fp)
+      if (!fp)
          goto error;
 
       /* Regarding setvbuf:
@@ -269,6 +266,7 @@ libretro_vfs_implementation_file *retro_vfs_file_open_impl(const char *path, uns
        * Since C89 does not support specifying a null buffer with a non-zero size, we create and track our own buffer for it.
        */
       /* TODO: this is only useful for a few platforms, find which and add ifdef */
+      stream->fp  = fp;
       stream->buf = (char*)calloc(1, 0x4000);
       setvbuf(stream->fp, stream->buf, _IOFBF, 0x4000);
    }

menu/drivers/xmb.c

@@ -1065,7 +1065,7 @@ static void xmb_update_thumbnail_path(void *data, unsigned i)
             sizeof(new_path));
 
 end:
-   if (!string_is_empty(new_path))
+   if (xmb && !string_is_empty(new_path))
       xmb->thumbnail_file_path = strdup(new_path);
    menu_entry_free(&entry);
 }