mt2: Allow breakfast sync to succeed if no vendor

Maintainers are of different opinions on this, but I'm in the camp of
letting breakfast finish error-free when initially syncing a device.
Vendor can be populated subsequent to device sync.

Change-Id: I1e203fb5c6ff3dcc24156b1681ebcee28345e591

mt2.mk

@@ -190,4 +190,4 @@ PRODUCT_PACKAGES += \
 $(call inherit-product,frameworks/native/build/phone-xhdpi-2048-dalvik-heap.mk)
 
 # inherit from the non-open-source side, if present
-$(call inherit-product, vendor/huawei/mt2/mt2-vendor.mk)
+$(call inherit-product-if-exists, vendor/huawei/mt2/mt2-vendor.mk)