Adjusted oggpack_writeinit() to not crash if malloc() return NULL.

Inspired by proposal in xiph#91.

(cherry picked from commit 8f30730)

Author: petterreinholdtsen

doc/libogg/oggpack_writeinit.html

@@ -39,8 +39,10 @@ <h3>Parameters</h3>
 
 <h3>Return Values</h3>
 <blockquote>
-<li>
-No values are returned.</li>
+<p>No values are returned.  If initialization fail, the buffer is
+  unusable and calls to
+  <a href="oggpack_writecheck.html">oggpack_writecheck()</a> will
+  report the error.</p>
 </blockquote>
 <p>
 

src/bitwise.c

@@ -39,6 +39,8 @@ static const unsigned int mask8B[]=
 void oggpack_writeinit(oggpack_buffer *b){
   memset(b,0,sizeof(*b));
   b->ptr=b->buffer=_ogg_malloc(BUFFER_INCREMENT);
+  if (!b->buffer)
+    return;
   b->buffer[0]='\0';
   b->storage=BUFFER_INCREMENT;
 }