This does not revert commit 950a5300 but applies the most
minimal hotfix I could come up with.
The reason for the breakage is that MWParameterPlaceholderPage
& MWParameterSearchWidget both hold references to the
MWTemplateModel. This model is not always the same. The dialog
might be the same when a template is edited multiple times.
But the model might be a new one. From this point on the
MWParameterSearchWidget pulls data from an outdated model.
This extra check compares this model reference and creates a
new widget when it changed.
Bug: T284636
Bug: T285571
Change-Id: Ib3eca52bbff90ffbf56a257e3984adcbe02b310b
6b346442ad