r.viewshed: initialize struct member before using struct

[ymdatta]

This was reported by cppcheck tool. Technically, we are not using the member in the struct variable in any of the subsequent functions, but it's a good practice to initialize all the struct members whenever possible.

Initial errors from cppcheck tool:

After applying the patch:

Additional information:

1. Machine used: Virtual Machine running Ubuntu 22.04.4 LTS.
2. Reproduction rate: 100%, reproducible every time.
3. Architecture: Not specific to any underlying architecture.

Testing done:

Ran the complete test_r_viewshed.py gunittest from the testsuite and it was successful.

[echoix]

What's the reasoning for using -1 as the initial value for angle? (I understand that 0 is a valid value that might cause confusion)

[ymdatta]

I wanted a value that's different from 0 and in the same module, I saw usage of -1 in two places for initialization: grass.cpp:L242 and grass.cpp:L460. So, I went ahead with -1.

[echoix]

grass/raster/r.viewshed/eventlist.h

Lines 49 to 60 in 5719ba6

	typedef struct event_ {
	dimensionType row, col; // location of the center of cell
	// 3 elevation values:
	// elev[0]: entering
	// elev[1]: center
	// elev[2]: exiting
	surface_type elev[3]; // elevation here
	double angle;
	char eventType;
	// type of the event: ENTERING_EVENT, EXITING_EVENT, CENTER_EVENT
	} AEvent;

I see here that the angle is a double. Should the suggestion of using -1.0 (like using 0.0 instead of 0) be applied here too, even if you pointed out occurrences where -1 was used (without the dot zero)?

[ymdatta]

I agree with you, I think -1.0 is the right literal to be used here. I have made the changes. Thanks!