MemoryTracking: adjust initialization calling

Calling of curl_memdebug() was still done with a pending free()

lib/memdebug.c

@@ -119,7 +119,7 @@ static long memsize = 0;  /* set number of mallocs allowed */
 void curl_memdebug(const char *logname)
 {
   if(!logfile) {
-    if(logname)
+    if(logname && *logname)
       logfile = fopen(logname, "w");
     else
       logfile = stderr;

lib/memdebug.h

@@ -32,14 +32,12 @@
 
 #include <curl/curl.h>
 
-#ifdef HAVE_SYS_TYPES_H
-#include <sys/types.h>
-#endif
-
 #ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
 #endif
 
+#define CURL_MT_LOGFNAME_BUFSIZE 512
+
 #define logfile curl_debuglogfile
 
 extern FILE *logfile;