show search button when structured search is modified

[bestchai]

To reproduce:

1. perform a structured search
2. click on 'structured search' and modify the sub-graph
3. notice that the 'search' button remains invisible -- the 'instances in view' still appears on the right

If you repeat the steps above with with keyword search, then when you modify the search bar text (in step 2), the 'search' button will appear on the right (counter to step 3). Structured search should behave identically.

[Issue created by bestchai: 2015-08-22]