xdu.c: Fixes need to compile xdu.c with -O2

I've choosen 'n/a' as initial string, because this clearly isn't
a filename.

xdu.c

@@ -999,7 +999,7 @@ void savepschildren(FILE* fp, struct node* nodep, struct rect rect, int showsize
         height,
         top;
     struct node* np;
-    char *name,
+    char *name="n/a",
         label[1024];
     struct rect subrect;
 
@@ -1148,7 +1148,7 @@ void fprintsvgnode(FILE* fp, struct rect rect)
 void fprintsvgnodetext(FILE* fp, int x, int y, long long size, char* name, int showsize)
 {
     char buffer[1024],
-        *text;
+        *text="n/a";
 
     switch (showsize) {
     case 0: