Prevent Lockscreen album art from activating FLAG_KEEP_SCREEN_ON

This is a small fix to the showWallpaper method, in which a power
consumption problem has been introduced. This showWallpaper method
toggles the window flag FLAG_SHOW_WALLPAPER, when album art is being
shown in Lockscreen. It is important to set pixel format to
PixelFormat.OPAQUE if flag FLAG_SHOW_WALLPAPER is not being set.

If not, an application that uses window flag FLAG_KEEP_SCREEN_ON
will prevent the keyguard from going to sleep and drain battery.

Change-Id: I1808be28047977ae5ac4dd1168ea25cac8a55a78
Frameworks: fix possible NPE + and missing expandable panel

Steps to reproduce for NPE:
- go into volume style settings
- switch to disabled
- switch to expanded
- NPE and hotreboot

Fix:
Check if mStreamControls is initialized and if not lock it and do it.

Steps for expandable error:
- go into volume style settings
- switch to disable
- press one time the volume button
- change to expandable
- change the volume and press the expanded icon
- result is it does not expand and is empty due of the missing volume panels.

Fix:
- if it was changed from disabled to expanded be sure that the additional volume panels
are recreated.

PS:
- fix another exception

Change-Id: I58d63d34f831b6a6f60f6eddb3a07fc916d464f3
Add missed string for Immersive Mode