Fix tests broken by r44880.

pkg/analyzer/lib/src/generated/ast.dart

Index: pkg/analyzer/lib/src/generated/ast.dart
diff --git a/pkg/analyzer/lib/src/generated/ast.dart b/pkg/analyzer/lib/src/generated/ast.dart
index 40fd83a45bf4f7ba69491c9f19b7266d3fa30e91..4bb900db81b67f88cc4cc015bf00405a512cfe03 100644
--- a/pkg/analyzer/lib/src/generated/ast.dart
+++ b/pkg/analyzer/lib/src/generated/ast.dart
@@ -16730,11 +16730,13 @@ class StringLexemeHelper {
     }
     end = lexeme.length;
     if (isLast) {
-      if (StringUtilities.endsWith3(lexeme, 0x22, 0x22, 0x22) ||
-          StringUtilities.endsWith3(lexeme, 0x27, 0x27, 0x27)) {
+      if (start + 3 <= end &&
+          (StringUtilities.endsWith3(lexeme, 0x22, 0x22, 0x22) ||
+              StringUtilities.endsWith3(lexeme, 0x27, 0x27, 0x27))) {
         end -= 3;
-      } else if (StringUtilities.endsWithChar(lexeme, 0x22) ||
-          StringUtilities.endsWithChar(lexeme, 0x27)) {
+      } else if (start + 1 <= end &&
+          (StringUtilities.endsWithChar(lexeme, 0x22) ||
+              StringUtilities.endsWithChar(lexeme, 0x27))) {
         end -= 1;
       }
     }