Fix crash in regexp/order-in-character-class rule (#52)

Author: ota-meshi

lib/rules/order-in-character-class.ts

@@ -271,7 +271,7 @@ function isNeedEscape(
     }
     const parent = target.parent as CharacterClass
     const prev = parent.elements[parent.elements.indexOf(target) - 1]
-    if (prev.type !== "Character" && prev.type !== "CharacterSet") {
+    if (!prev || (prev.type !== "Character" && prev.type !== "CharacterSet")) {
         return false
     }
     return true

tests/lib/rules/order-in-character-class.ts

@@ -178,5 +178,12 @@ tester.run("order-in-character-class", rule as any, {
                 "Expected character class elements to be in ascending order. '-' should be before 'a-b'.",
             ],
         },
+        {
+            code: String.raw`/[a-b-]/u`,
+            output: String.raw`/[-a-b]/u`,
+            errors: [
+                "Expected character class elements to be in ascending order. '-' should be before 'a-b'.",
+            ],
+        },
     ],
 })