Context menu sometimes errors and won't show up

[bbondy]

Both @alexwykoff and I reproduced this only once sometimes right clicking in an input field would hit sanitize menu items with a 0 length array. Not passing in an initial value for 0 length arrays errors so the context menu was being suppressed.

2:2262:0202/152618:ERROR:CONSOLE(41)] "Uncaught TypeError: Reduce of empty array with no initial value", source:  

Error in this function:

const reduced = template.reduce((previousValue, currentValue, currentIndex, array) => {

QA steps to test:

• Just make sure that context menus work the same way as they did in 0.12.15 in general.