Support optional catch binding

[cixel]

Support this Stage 4 proposal to allow omission of catch variable in cases where the error is unused:

try {
  // ...
} catch {
  // ...
}

See Why? for justification and more details.

This has already been implemented in v8 6.6 and is available in recent versions of Chrome and in Node.js 10.

To reproduce

escodegen.generate({
  type: 'TryStatement',
  block: {
    type: 'BlockStatement',
    body: []
  },
  handler: {
    type: 'CatchClause',
    param: null,
    body: {
      type: 'BlockStatement',
      body: []
    }
  },
  finalizer: null
})

Output

/Users/ehdens/misc-oss/escodegen/escodegen.js:2446
        type = expr.type || Syntax.Property;
                    ^

TypeError: Cannot read property 'type' of null
    at CodeGenerator.generateExpression (/Users/ehdens/misc-oss/escodegen/escodegen.js:2446:21)
    at /Users/ehdens/misc-oss/escodegen/escodegen.js:1181:26
    at withIndent (/Users/ehdens/misc-oss/escodegen/escodegen.js:574:9)
    at CodeGenerator.CatchClause (/Users/ehdens/misc-oss/escodegen/escodegen.js:1176:13)
    at CodeGenerator.generateStatement (/Users/ehdens/misc-oss/escodegen/escodegen.js:2465:33)
    at CodeGenerator.TryStatement (/Users/ehdens/misc-oss/escodegen/escodegen.js:1526:52)
    at CodeGenerator.generateStatement (/Users/ehdens/misc-oss/escodegen/escodegen.js:2465:33)
    at generateInternal (/Users/ehdens/misc-oss/escodegen/escodegen.js:2486:28)
    at Object.generate (/Users/ehdens/misc-oss/escodegen/escodegen.js:2554:18)
    at Object.<anonymous> (/Users/ehdens/misc-oss/escodegen/demo.js:3:24)

Expected Output

try {
} catch {
}

[sanex3339]

Support in master now