cmd: Avoid execution if block misses closing brackets.

programs/cmd/tests/test_builtins.cmd

@@ -1055,6 +1055,30 @@ if 1 == 0 (
 @tab@
 @tab@
 ) else echo block containing two lines with just tab seems to work
+::
+echo @if 1 == 1 (> blockclosing.cmd
+echo   echo with closing bracket>> blockclosing.cmd
+echo )>> blockclosing.cmd
+cmd.exe /Q /C blockclosing.cmd
+echo %ERRORLEVEL% ok
+::
+echo @if 1 == 1 (> blockclosing.cmd
+echo   echo without closing bracket first>> blockclosing.cmd
+echo   echo without closing bracket second>> blockclosing.cmd
+cmd.exe /Q /C blockclosing.cmd
+echo %ERRORLEVEL% two lines
+::
+echo echo before both blocks> blockclosing.cmd
+echo @if 1 == 1 (>> blockclosing.cmd
+echo   echo before nested block without closing bracket>> blockclosing.cmd
+echo   @if 2 == 2 (>> blockclosing.cmd
+echo     echo without closing bracket>> blockclosing.cmd
+echo )>> blockclosing.cmd
+echo echo outside of block without closing bracket>> blockclosing.cmd
+cmd.exe /Q /C blockclosing.cmd
+echo %ERRORLEVEL% nested
+::
+del blockclosing.cmd
 echo --- case sensitivity with and without /i option
 if bar==BAR echo if does not default to case sensitivity
 if not bar==BAR echo if seems to default to case sensitivity

programs/cmd/tests/test_builtins.cmd.exp

@@ -713,6 +713,11 @@ block containing a line with just space and tab seems to work
 block containing a line with just tab and space seems to work
 block containing two lines with just space seems to work
 block containing two lines with just tab seems to work
+with closing bracket
+0 ok
+255 two lines
+before both blocks
+255 nested
 --- case sensitivity with and without /i option
 if seems to default to case sensitivity
 if /i seems to work

programs/cmd/wcmdmain.c

@@ -2347,6 +2347,13 @@ WCHAR *WCMD_ReadAndParseLine(const WCHAR *optionalcmd, CMD_LIST **output, HANDLE
       }
     }
 
+    if (curDepth > lineCurDepth) {
+        WINE_TRACE("Brackets do not match, error out without executing.\n");
+        WCMD_free_commands(*output);
+        *output = NULL;
+        errorlevel = 255;
+    }
+
     /* Dump out the parsed output */
     WCMD_DumpCommands(*output);