Fix panic when a module has an invalid output path

dep.OutputFile().Path() can panic if the OutputFile
is invalid, so move more of the code into the check
for validity. This changes the go crash into a
build error.

Bug: 158624492
Test: Apply the patchset 1 of ag/11815659, lunch aosp_x86_64-eng, m
Change-Id: Ic8a728be1b570ac73be7b2b9461676f9fd99c266