Update SA1008 to not crash if there is no token before the analyzed opening parenthesis

#2354

Author: bjornhellander

StyleCop.Analyzers/StyleCop.Analyzers.Test/SpacingRules/SA1008UnitTests.cs

@@ -2158,5 +2158,22 @@ public void TestMethod()
 
             await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(2354, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/2354")]
+        public async Task TestNoPreviousTokenAsync()
+        {
+            var testCode = "(";
+
+            var test = new CSharpTest()
+            {
+                TestCode = testCode,
+
+                // Compiler diagnostics differ between Roslyn versions. The main thing is that the analyzer doesn't throw an exception.
+                CompilerDiagnostics = CompilerDiagnostics.None,
+            };
+
+            await test.RunAsync(CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1008OpeningParenthesisMustBeSpacedCorrectly.cs

@@ -100,6 +100,9 @@ private static void HandleOpenParenToken(SyntaxTreeAnalysisContext context, Synt
             bool precededByKeyword;
             switch (prevToken.Kind())
             {
+            case SyntaxKind.None:
+                return;
+
             case SyntaxKind.AwaitKeyword:
             case SyntaxKind.CaseKeyword:
             case SyntaxKind.CatchKeyword: