opened
shreyanshdwivedi
username_0
Fixes #8547 

**Testing Plan:** I used the developer tool and git grep to find area of the relevant code. Then, I used js to test different cases.
I disabled the `Reply` button when the `stream` or `topic` or `pm` is not having any message, which restores its normal behaviour when it encounters the same with messages or when we go to `Home`,

**GIFs or Screenshots:** 
![ezgif com-video-to-gif 9](https://user-images.githubusercontent.com/25428397/36937887-ee401bae-1f3f-11e8-81d0-f388668f7697.gif)
compose: Reply button becomes inactive when there are no messages.
issue