Do not start pasls without valid PP

.vscode/settings.json

@@ -20,6 +20,7 @@
         "markdowndescription",
         "pasls",
         "spammy",
+        "Testcase",
         "theangryepicbanana",
         "Typecheck",
         "unregisters",

src/castleConfiguration.js

@@ -362,7 +362,6 @@ class CastleConfiguration {
 
         // exit with clear error message when FPC compiler not found
         if (fpcExe === '') {
-
             vscode.window.showErrorMessage('FPC compiler executable not configured and not found on the PATH. Configure the FPC compiler location in the extension settings.');
             return;
         }

src/castlePascalLanguageServer.js

@@ -46,6 +46,14 @@ class CastlePascalLanguageServer {
         this.environmentForPascalServer['FPCTARGET'] = this._castleConfig.fpcTargetOs;
         this.environmentForPascalServer['FPCTARGETCPU'] = this._castleConfig.fpcTargetCpu;
 
+        /* pasls cannot work without FPC executable.
+           Testcase: without this line, editing settings of PP back and forth
+           from valid to invalid FPC executable location, would cause a number
+           of errors that pasls cannot be stopped because it is still starting. */
+        if (this._castleConfig.fpcExecutablePath === '') {
+            return false;
+        }
+
         /* We need to set environment variable CASTLE_ENGINE_PATH, this is
            how we pass engine path (maybe from $CASTLE_ENGINE_PATH, maybe from
            VS extension config) to pasls. */