Validate find_pkgname before use it.

Validate find_pkgname before use it.

If a user calls set_extra_info function before create a window,
it will access the uninitialized function pointer.

To guide them to do not use this API before creating window is not enough.
So this patch should need to be applied. to prevent from unexpected crash issue.

[model] Redwood,Kiran,B3(Wearable)
[binary_type] AP
[customer] Docomo/Orange/ATT/Open
[issue#] N/A
[problem]
[cause]
[solution]
[team] HomeTF
[request]
[horizontal_expansion]

Change-Id: I53468147ba4339557a7b4f59c3c5d32bcc6805a1