make: version -- Ensure that .gitid exist vefore read

In case if there is no .gitid file we might endup
with build error. Make sure it exist.
Reported-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

scripts/Makefile.version

@@ -7,7 +7,7 @@ GITID := $(shell if [ -d ".git" ]; then git describe; fi)
 ifeq ($(GITID),)
 	GITID := 0
 else
-        GITID_FILE_VALUE := $(shell if [ `cat .gitid` = $(GITID) ]; then echo y; fi)
+        GITID_FILE_VALUE := $(shell if [ -f '.gitid' ]; then if [ `cat .gitid` = $(GITID) ]; then echo y; fi; fi)
         ifneq ($(GITID_FILE_VALUE),y)
                 .PHONY: $(GITID_FILE)
         endif