When asked to malloc zero bytes, malloc one byte instead. This ensures

that we get a unique pointer rather than NULL (which ANSI C otherwise permits).
Problem pointed out by Mike Protts.

[originally from svn r6308]

misc.c

@@ -441,6 +441,7 @@ void *safemalloc(size_t n, size_t size)
 	p = NULL;
     } else {
 	size *= n;
+	if (size == 0) size = 1;
 #ifdef MINEFIELD
 	p = minefield_c_malloc(size);
 #else