Fix running if built on OS X 10.9

strncpy with in == out causes signal 6 if built on OS X 10.9.
(If built on older OS X versions, the game works on 10.9 though.)

It was happening in COM_StripExtension during map load.

code/qcommon/q_shared.c

@@ -76,8 +76,12 @@ COM_StripExtension
 void COM_StripExtension( const char *in, char *out, int destsize )
 {
 	const char *dot = strrchr(in, '.'), *slash;
+
 	if (dot && (!(slash = strrchr(in, '/')) || slash < dot))
-		Q_strncpyz(out, in, (destsize < dot-in+1 ? destsize : dot-in+1));
+		destsize = (destsize < dot-in+1 ? destsize : dot-in+1);
+
+	if ( in == out && destsize > 1 )
+		out[destsize-1] = '\0';
 	else
 		Q_strncpyz(out, in, destsize);
 }