qemu-img: Plug memory leak on block option help error path

Introduced in commit a283cb6; mostly harmless.  Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qemu-img.c

@@ -287,6 +287,7 @@ static int print_block_option_help(const char *filename, const char *fmt)
         proto_drv = bdrv_find_protocol(filename, true);
         if (!proto_drv) {
             error_report("Unknown protocol '%s'", filename);
+            free_option_parameters(create_options);
             return 1;
         }
         create_options = append_option_parameters(create_options,