remove useless if-before-free tests.

remove useless if-before-free tests.

E.g., in this example, the "if (p)" test is useless.

  if (p)
    free (p);

I've been removing such tests systematically.
Here's where I proposed it to the git folks, along with justification
for why it's ok to perform this transformation, these days (no one
uses SunOS4 anymore):

    http://thread.gmane.org/gmane.comp.version-control.git/74187

Signed-off-by: Jim Meyering <meyering@redhat.com>