Remove unnecessary null pointer tests to avoid a false Coverity FORWARD_NULL defect.
Remove unnecessary null pointer tests to avoid a false Coverity
FORWARD_NULL defect.

In the for loop, at most one buffer in the |buffers| array
is of type SECBUFFER_DATA and at most one is of type SECBUFFER_EXTRA.
The null pointer test for decrypted_ptr_ is not necessary because
when we encounter the only buffer of type SECBUFFER_DATA, decrypted_ptr_
must be NULL (the initial value).  I added a DCHECK to assert that.
Similarly the null pointer test for received_ptr_ is not necessary.

R=mattm
BUG=22286
CID=5331
TEST=one
Review URL: http://codereview.chromium.org/371014

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@31499 0039d316-1c4b-4281-b951-d872f2087c98

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