Fix initial setting of LCB editor pref

The following command sequence (in message box):
`put revIDEGetPreference("LCB_textEditor") into tEditor; launch ".../treeviewx.lcb" with tEditor; put the result`
Results in the value of `tEditor` when successful (although success in opening the file is not guaranteed)

Added a check for "no such program" in the case where the specified editor is no longer available
Updated code to use the `tEditor` variable in place of `it` for clarity
Added a check for `tResult` being `tEditor` to not display an error

Author: bwmilby

Toolset/libraries/revidedeveloperextensionlibrary.livecodescript

@@ -593,19 +593,21 @@ on revIDEDeveloperExtensionEditScript pFolder
       end if
    end if
 
-   if tResult is "no association" or tResult is "request failed" then
+   if tResult is "no association" or tResult is "request failed" \
+         or tResult is "no such program" then
       answer file "Select text editor..."
-      if it is not empty then
-         launch tFile with it
+      put it into tEditor
+      if tEditor is not empty then
+         launch tFile with tEditor
          put the result into tResult
          if tResult is empty then
             # AL-2015-04-01: [[ Bug 15130 ]] If the new text editor launch was successful, set the preference
-            revIDESetPreference "LCB_textEditor", it
+            revIDESetPreference "LCB_textEditor", tEditor
          end if
       end if
    end if
 
-   if tResult is not empty then
+   if tResult is not empty and tResult is not tEditor then
       __revIDEDeveloperExtensionSendError "Could not open" && tFile & ":" && tResult
    end if
 end revIDEDeveloperExtensionEditScript