pkg-generic: run $(PKG)_PRE_RSYNC_HOOKS before checking for the existence of $(SRCDIR)

This will allow packages to define their pre-rsync hooks which will be
guaranteed to run even if the source is missing.

Signed-off-by: Tal Shorer <tal.shorer@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pkg-generic.mk

@@ -161,8 +161,8 @@ $(BUILD_DIR)/%/.stamp_extracted:
 # used.
 $(BUILD_DIR)/%/.stamp_rsynced:
 	@$(call MESSAGE,"Syncing from source dir $(SRCDIR)")
-	@test -d $(SRCDIR) || (echo "ERROR: $(SRCDIR) does not exist" ; exit 1)
 	$(foreach hook,$($(PKG)_PRE_RSYNC_HOOKS),$(call $(hook))$(sep))
+	@test -d $(SRCDIR) || (echo "ERROR: $(SRCDIR) does not exist" ; exit 1)
 	rsync -au --chmod=u=rwX,go=rX $(RSYNC_VCS_EXCLUSIONS) $(call qstrip,$(SRCDIR))/ $(@D)
 	$(foreach hook,$($(PKG)_POST_RSYNC_HOOKS),$(call $(hook))$(sep))
 	$(Q)touch $@