cmd: Fix tilda parameter expansion when arg is empty.

programs/cmd/batch.c

@@ -514,11 +514,13 @@ void WCMD_HandleTildaModifiers(WCHAR **start, BOOL atExecute)
   /* After this, we need full information on the file,
     which is valid not to exist.  */
   if (!skipFileParsing) {
-    if (GetFullPathNameW(outputparam, MAX_PATH, fullfilename, NULL) == 0)
-      return;
-
-    exists = GetFileAttributesExW(fullfilename, GetFileExInfoStandard,
-                                  &fileInfo);
+    if (GetFullPathNameW(outputparam, MAX_PATH, fullfilename, NULL) == 0) {
+      exists = FALSE;
+      fullfilename[0] = 0x00;
+    } else {
+      exists = GetFileAttributesExW(fullfilename, GetFileExInfoStandard,
+                                    &fileInfo);
+    }
 
     /* 2. Handle 'a' : Output attributes (File doesn't have to exist) */
     if (memchrW(firstModifier, 'a', modifierLen) != NULL) {

programs/cmd/tests/test_builtins.cmd

@@ -363,6 +363,7 @@ for %%i in ("d e" f) do echo %%~dpi
 for %%i in ("g h" i) do echo %%~sdi
 for %%i in ("g h" i) do echo %%~dsi
 for %%i in ("j k" l.eh) do echo '%%~xsi'
+for %%i in ("") do echo '%%~i,%%~fi,%%~di,%%~pi,%%~ni,%%~xi,%%~si,%%~ai,%%~ti,%%~zi'
 
 echo --- in parameters
 for %%i in ("A B" C) do call :echoFun %%i

programs/cmd/tests/test_builtins.cmd.exp

@@ -319,6 +319,7 @@ N
 @drive@
 ''
 '.eh'
+',,,,,,,,,'
 --- in parameters
 "A B"
 C