camera: Restart preview after ZSL changes only if the preview is running

Don't touch the preview state if it was stopped to begin with

Change-Id: Ie81c01165778f98f92f11badc17c2023ea4610b7
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_device_lge_g2-common into kk_mkt