xbps-src: only run bootstrap-update with -t.

xbps-src

@@ -612,8 +612,10 @@ case "$XBPS_TARGET" in
     fetch|extract|build|configure|install|pkg)
         BEGIN_INSTALL=1
         read_pkg
-        bootstrap_update
-        create_temporary_masterdir
+        if [ -n "$XBPS_TEMP_MASTERDIR" ]; then
+            bootstrap_update
+            create_temporary_masterdir
+        fi
         if [ -n "$CHROOT_READY" -a -z "$IN_CHROOT" ]; then
             chroot_handler $XBPS_TARGET $XBPS_TARGET_PKG
         else