mextra follow up bit 2

<Someone> noticed the leftover zeromextra, this removes it.

Using memset() on a possibly failed mextra allocation was inapprorpriate,
so replace the newmextra() macro with a function.

Prevent a crash in christen_monst() if mextra was not initialized.

src/do_name.c

@@ -233,6 +233,7 @@ const char *name;
 		return mtmp;
 	}
 	if (has_name(mtmp)) free((genericptr_t)MNAME(mtmp));
+	if (!mtmp->mextra) mtmp->mextra = newmextra();
 
 	MNAME(mtmp) = (char *)alloc(lth);
 	if (lth) Strcpy(MNAME(mtmp), name);

src/makemon.c

@@ -9,7 +9,6 @@
 #endif
 
 STATIC_VAR NEARDATA struct monst zeromonst;
-STATIC_VAR NEARDATA struct mextra zeromextra;
 
 /* this assumes that a human quest leader or nemesis is an archetype
    of the corresponding role; that isn't so for some roles (tourist
@@ -853,6 +852,16 @@ int mndx;
     }
 }
 
+struct mextra *
+newmextra()
+{
+	struct mextra *mextra;
+	mextra = (struct mextra *)alloc(sizeof(struct mextra));
+	if (mextra)
+	    (void) memset((genericptr_t)mextra, 0, sizeof(struct mextra));
+	return mextra;
+}
+
 /*
  * called with [x,y] = coordinates;
  *	[0,0] means anyplace