block: Fix leak in bdrv_create_file_fallback()

@options is leaked by the first two return statements in this function.

Note that blk_new_open() takes the reference to @options even on
failure, so all we need to do to fix the leak is to move the QDict
allocation down to where we actually need it.

Reported-by: Coverity (CID 1419884)
Fixes: fd17146
       ("block: Generic file creation fallback")
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200225155618.133412-1-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -600,7 +600,7 @@ static int bdrv_create_file_fallback(const char *filename, BlockDriver *drv,
                                      QemuOpts *opts, Error **errp)
 {
     BlockBackend *blk;
-    QDict *options = qdict_new();
+    QDict *options;
     int64_t size = 0;
     char *buf = NULL;
     PreallocMode prealloc;
@@ -623,6 +623,7 @@ static int bdrv_create_file_fallback(const char *filename, BlockDriver *drv,
         return -ENOTSUP;
     }
 
+    options = qdict_new();
     qdict_put_str(options, "driver", drv->format_name);
 
     blk = blk_new_open(filename, NULL, options,