param_feerate: parse numbers correctly.

If you used feerate=750, instead of feerate="750" it didn't work, since the
token is not a string.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: JSON RPC: `withdraw` and `txprepare` `feerate` can be a JSON number.

common/json_tok.c

@@ -355,7 +355,7 @@ struct command_result *param_feerate_val(struct command *cmd,
 				    buffer + base.start);
 	}
 
-	if (json_tok_streq(buffer, &suffix, "")
+	if (suffix.end == suffix.start
 	    || json_tok_streq(buffer, &suffix,
 			      feerate_style_name(FEERATE_PER_KBYTE))) {
 		style = FEERATE_PER_KBYTE;