procinfo: do null check before setting error string. am: 3dbe823a2a

Original change: https://android-review.googlesource.com/c/platform/system/libprocinfo/+/1710944

Change-Id: I6756441529d6bbb9a41a15a44fbb68256cbdd649
tree: 6b2000fa0bafa5a0e27b839d62c2e29c63428375
  1. include/
  2. testdata/
  3. Android.bp
  4. OWNERS
  5. process.cpp
  6. process_map_benchmark.cpp
  7. process_map_test.cpp
  8. process_test.cpp