Avoid calling libc realloc with a requested size of zero.

ChangeLog

 2012-09-16  Niels Möller  <nisse@lysator.liu.se>
 
+	* realloc.c (nettle_realloc): Only call libc realloc if length >
+	0, otherwise call free. Fixes a small memory leak.
+	(nettle_xrealloc): Likewise.
+
 	* run-tests (test_program): Don't quote $EMULATOR; allow it to
 	expand to program and arguments (e.g., valgrind).
 

realloc.c

@@ -31,20 +31,32 @@
 
 #include "realloc.h"
 
+/* NOTE: Calling libc realloc with size == 0 is not required to
+   totally free the object, it is allowed to return a valid
+   pointer. */
 void *
 nettle_realloc(void *ctx UNUSED, void *p, unsigned length)
 {
+  if (length > 0)
     return realloc(p, length);
+
+  free(p);
+  return NULL;
 }
 
 void *
 nettle_xrealloc(void *ctx UNUSED, void *p, unsigned length)
+{
+  if (length > 0)
     {
       void *n = realloc(p, length);
-  if (length && !n)
+      if (!n)
 	{
 	  fprintf(stderr, "Virtual memory exhausted.\n");
 	  abort();
 	}
       return n;
     }
+  free(p);
+  return NULL;
+}