remote-ext: do not segfault for blank lines

Instead of stripping space characters past the beginning of the
line and overflowing a buffer, stop at the beginning of the line
(mimicking the corresponding fix in remote-fd).

The argument to isspace does not need to be cast explicitly because
git isspace takes care of that already.

Noticed-by: Junio C Hamano <[email protected]>
Signed-off-by: Jonathan Nieder <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jrn

builtin/remote-ext.c

@@ -212,16 +212,16 @@ static int command_loop(const char *child)
 	char buffer[MAXCOMMAND];
 
 	while (1) {
-		size_t length;
+		size_t i;
 		if (!fgets(buffer, MAXCOMMAND - 1, stdin)) {
 			if (ferror(stdin))
 				die("Comammand input error");
 			exit(0);
 		}
 		/* Strip end of line characters. */
-		length = strlen(buffer);
-		while (isspace((unsigned char)buffer[length - 1]))
-			buffer[--length] = 0;
+		i = strlen(buffer);
+		while (i > 0 && isspace(buffer[i - 1]))
+			buffer[--i] = 0;
 
 		if (!strcmp(buffer, "capabilities")) {
 			printf("*connect\n\n");