Avoid crashing on valueless boolean props

b8217ed removed the node.value check
leading to this crashing on any valueless boolean prop such as
<Component isWhatever />

This just readds the check.

Author: reosarevok

lib/rules/jsx-no-literals.js

@@ -503,9 +503,9 @@ module.exports = {
       },
 
       JSXAttribute(node) {
-        const isLiteralString = node.value.type === 'Literal'
+        const isLiteralString = node.value && node.value.type === 'Literal'
           && typeof node.value.value === 'string';
-        const isStringLiteral = node.value.type === 'StringLiteral';
+        const isStringLiteral = node.value && node.value.type === 'StringLiteral';
 
         if (isLiteralString || isStringLiteral) {
           const resolvedConfig = getOverrideConfig(node) || config;