fix(nsis): Error handling if uninstaller cannot be launched (#4674)

This adds error handling if the old-uninstaller.exe process cannot be
launched. Previously the error flag was not checked after calling
ExecWait (ifErrors was missing).

In case old-uninstaller.exe cannot be launched from inside $PLUGINSDIR
(a.k.a a subfolder of the Temp directory) - for example due to a group policy
restriction that prevents executables from being launched that reside
inside the Temp folder - the original uninstaller residing inside the
application install directory is executed in place.

If this still fails the update is aborted.

packages/app-builder-lib/templates/nsis/include/installUtil.nsh

@@ -108,6 +108,7 @@ Var /GLOBAL isTryToKeepShortcuts
 # http://stackoverflow.com/questions/24595887/waiting-for-nsis-uninstaller-to-finish-in-nsis-installer-either-fails-or-the-uni
 Function uninstallOldVersion
   Var /GLOBAL uninstallerFileName
+  Var /Global uninstallerFileNameTemp
   Var /GLOBAL installationDir
   Var /GLOBAL uninstallString
   Var /GLOBAL rootKey
@@ -142,9 +143,6 @@ Function uninstallOldVersion
     Goto Done
   ${endif}
 
-  !insertmacro copyFile "$uninstallerFileName" "$PLUGINSDIR\old-uninstaller.exe"
-  StrCpy $uninstallerFileName "$PLUGINSDIR\old-uninstaller.exe"
-
   ${if} $installMode == "CurrentUser"
   ${orIf} $rootKey == "HKEY_CURRENT_USER"
     StrCpy $0 "/currentuser"
@@ -170,7 +168,20 @@ Function uninstallOldVersion
     StrCpy $0 "$0 --updated"
   ${endif}
 
-  ExecWait '"$uninstallerFileName" /S /KEEP_APP_DATA $0 _?=$installationDir' $R0
+  StrCpy $uninstallerFileNameTemp "$PLUGINSDIR\old-uninstaller.exe"
+  !insertmacro copyFile "$uninstallerFileName" "$uninstallerFileNameTemp"
+
+  ExecWait '"$uninstallerFileNameTemp" /S /KEEP_APP_DATA $0 _?=$installationDir' $R0
+  ifErrors 0 ExecErrorHandler
+    # the execution failed - might have been caused by some group policy restrictions
+    # we try to execute the uninstaller in place
+    ExecWait '"$uninstallerFileName" /S /KEEP_APP_DATA $0 _?=$installationDir' $R0
+    ifErrors 0 ExecErrorHandler
+      # this also failed...
+      DetailPrint `Aborting, uninstall was not successful. Not able to launch uninstaller!`
+      SetErrorLevel 5
+      Abort "Cannot uninstall"
+  ExecErrorHandler:
   ${if} $R0 != 0
     DetailPrint `Aborting, uninstall was not successful. Uninstaller error code: $R0.`
     SetErrorLevel 5