[Feature Request] Add format variable to detect presence of sensor readings

[NobodyXu]

Is your feature request related to a problem? Please describe.

Currently, swaystatus will print out uninitialized garbage if there is no sensor reading at all. Reading uninitialized garbage is undefined behavior and shall be fixed.

Describe the solution you'd like

Reading uninitialized data should be fixed and a format variable should be added to detect presence of sensor readings.