[SysInfo] Fixed the cellular attribute crash

The old implementation directly used 'NULL' as the parameter, which will result
in the crash when calling tapi function. Here, we use tel_init to produce the
TelHandle as the parameter and check the validity of the parameter in advance.

BUG=XWALK-1641
Merge pull request #307 from qjia7/master

[SysInfo] Fixed the cellular attribute crash