a empty string can be caused by a path like "\boot.ini", so support that as well

git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@5439 212acab6-be3b-0410-9dea-997c60f758d6

Source/exehead/util.c

@@ -140,7 +140,7 @@ void NSISCALL myDelete(char *buf, int flags)
       trimslashtoend(buf);
 
     // only append backslash if the path isn't relative to the working directory [bug #1851273]
-    if (*buf)
+    if (*buf || *lbuf == '\\')
       mystrcat(buf,"\\");
 
     fn=buf+mystrlen(buf);