Fix potential null pointer dereference.

Fix potential null pointer dereference.

If a MinidumpLinuxMapsList was created and destroyed without its Read method,
the program would have a segmentation fault because the destructor did not
check for a null maps_ field. Additional changes include additional
supplementary null checks, a potential memory leak fix, and some comment
removal.

Committed: https://code.google.com/p/google-breakpad/source/detail?r=1478

[liuandrew, 2015-07-31 15:14:08]

liu.andrew.x@gmail.com changed reviewers:
+ ahonig@google.com, ivanpe@chromium.org, mmandlis@chromium.org,
srutherford@google.com

[liuandrew, 2015-07-31 15:26:44]

Committed patchset #1 (id:1) manually as r1478 (presubmit successful).

[mmandlis, 2015-07-31 15:26:57]

lgtm