update_check.sh: do not check packages without distfiles

common/xbps-src/shutils/update_check.sh

@@ -11,6 +11,13 @@ update_check() {
     export LC_ALL=C
     : ${update_pkgname:=$pkgname}
 
+    if [ -z "$distfiles" ]; then
+        if [ -n "$XBPS_UPDATE_CHECK_VERBOSE" ]; then
+            echo "no distfiles to check for $pkgname"
+        fi
+        return
+    fi
+
     if [ -z "$update_site" ]; then
         printf '%s\n' "$homepage"
         for i in $distfiles; do