Windows: Fix rare cases being stuck in Secure Desktop after it is use…

…d for password entry

Cause seems to be IME as documented in KeePass project (https://keepass.info/help/kb/sec_desk.html#ime). We use the same approach as KeePass to disable IME in Secure Desktop.
This commit also add few changes:
  - we switch to secure desktop only if SetThreadDesktop succeeds
  - we call SwitchDesktop to switch to original desktop only if we actually succeeded in displaying secure desktop

src/Common/Dlgcode.c

@@ -13921,20 +13921,33 @@ static unsigned int __stdcall SecureDesktopThread( LPVOID lpThreadParameter )
  StringCbCopy(SecureDesktopName, sizeof (SecureDesktopName), pParam->szDesktopName);
  pParam->hDesk = hSecureDesk;
 
- // wait for SwitchDesktop to succeed before using it for current thread
- while (true)
+ bNewDesktopSet = SetThreadDesktop (hSecureDesk);
+
+ if (bNewDesktopSet)
  {
- if (SwitchDesktop (hSecureDesk))
+ // call ImmDisableIME　from imm32.dll to disable IME since it can create issue with secure desktop
+ // cf: https://keepass.info/help/kb/sec_desk.html#ime
+ HMODULE hImmDll = LoadLibraryEx (L"imm32.dll", NULL, LOAD_LIBRARY_SEARCH_SYSTEM32);
+ if (hImmDll)
  {
- break;
+ typedef BOOL (WINAPI *ImmDisableIME_t)(DWORD);
+ ImmDisableIME_t ImmDisableIME = (ImmDisableIME_t) GetProcAddress (hImmDll, "ImmDisableIME");
+ if (ImmDisableIME)
+ {
+ ImmDisableIME (0);
+ }
  }
- Sleep (SECUREDESKTOP_MONOTIR_PERIOD);
- }
 
- bNewDesktopSet = SetThreadDesktop (hSecureDesk);
+ // wait for SwitchDesktop to succeed before using it for current thread
+ while (true)
+ {
+ if (SwitchDesktop (hSecureDesk))
+ {
+ break;
+ }
+ Sleep (SECUREDESKTOP_MONOTIR_PERIOD);
+ }
 
- if (bNewDesktopSet)
- {
  // create the thread that will ensure that VeraCrypt secure desktop has always user input
  // this is done only if the stop event is created successfully
  HANDLE hStopEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
@@ -13964,6 +13977,12 @@ static unsigned int __stdcall SecureDesktopThread( LPVOID lpThreadParameter )
  }
 
  pParam->bDlgDisplayed = TRUE;
+
+ // free imm32.dll handle
+ if (hImmDll)
+ {
+ FreeLibrary (hImmDll);
+ }
  }
  else
  {
@@ -14084,19 +14103,20 @@ INT_PTR SecureDesktopDialogBoxParam(
  // dialog box was indeed displayed in Secure Desktop
  retValue = param.retValue;
  bSuccess = TRUE;
+
+ // switch back to the original desktop
+ while (!SwitchDesktop (hOriginalDesk))
+ {
+ Sleep (SECUREDESKTOP_MONOTIR_PERIOD);
+ }
+
+ SetThreadDesktop (hOriginalDesk);
  }
- }
 
- if (param.hDesk)
- { 
- while (!SwitchDesktop (hOriginalDesk))
+ if (param.hDesk)
  {
- Sleep (SECUREDESKTOP_MONOTIR_PERIOD);
+ CloseDesktop (param.hDesk);
  }
-
- SetThreadDesktop (hOriginalDesk);
-
- CloseDesktop (param.hDesk);
  }
 
  // get the new list of ctfmon.exe processes in order to find the ID of the