Ensure we clear magnification specs on non-magnifiable containers.

It seems it's possible the IME container could be magnified before an IME
is added. Once the IME is added we will view this as non-magnifiable and then
never un-do the magnification.

Bug: 137691821
Test: Manual
Change-Id: I39b43367ac500a5c6c330b5ae3a451345fa5aec4