xbps-src: if euid can't write to masterdir, exit gracefully.

xbps-src/xbps-src.sh.in

@@ -215,11 +215,9 @@ check_config_vars()
 			msg_error "'${f}' not set in configuration file!\n"
 		fi
 	done
-	if [ ! -d "$XBPS_MASTERDIR" ]; then
-		mkdir -p "$val"
-		if [ $? -ne 0 ]; then
-			msg_error "couldn't create 'XBPS_MASTERDIR' directory\n"
-		fi
+	if [ ! -w "$XBPS_MASTERDIR" ]; then
+		echo "ERROR: not enough perms for masterdir $XBPS_MASTERDIR.\n"
+		exit 1
 	fi
 	[ -z "${_MASTERDIR_FLAG}" ] && export _MASTERDIR="$XBPS_MASTERDIR"
 }