Fix uninitialized data members

When running under the address sanitizer, the first protobuf message the
frontend recieved would always contain all messages (zero-valued). So
always assign the booleans to false in the constructor.

Bug: 112421555
Test: ninja --frontend=.../ninja/frontend/dump.py   w/asan
Change-Id: I2c89e59121a5ca0918e13764187ea5797cfde7cb
2 files changed