color.c: trim leading spaces in color_parse_mem()

Normally color_parse_mem() is called from config parser which trims the
leading spaces already. The new caller in the next patch won't. Let's be
tidy and trim leading spaces too (we already trim trailing spaces
after a word).
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

color.c

@@ -207,10 +207,15 @@ int color_parse_mem(const char *value, int value_len, char *dst)
 	struct color fg = { COLOR_UNSPECIFIED };
 	struct color bg = { COLOR_UNSPECIFIED };
 
+	while (len > 0 && isspace(*ptr)) {
+		ptr++;
+		len--;
+	}
+
 	if (!len)
 		return -1;
 
-	if (!strncasecmp(value, "reset", len)) {
+	if (!strncasecmp(ptr, "reset", len)) {
 		xsnprintf(dst, end - dst, GIT_COLOR_RESET);
 		return 0;
 	}