Memory leak in matrix portion of math on-screen keyboard

[jaltekruse]

To reproduce, navigate to the matrix tab, open the dropdown to select end caps and then click away from the math keyboard entirely to close it. This error shows in the console.

Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
in MatrixSizePicker (at MathInput.js:466)
in div (at MathInput.js:464)
in div (at MathInput.js:351)
in TexButtons (at MathInput.js:515)