Fix graph black trail bug

[LeaNumworks]

Fixes #1458

The problem only appeared on the device and was not on the macOS simulator due to the different values of FLT_EPSILON: 1e-5 on the device, around 1e-7 on the simulator.

Now the cursor cannot be on the edge of the graph view: panToMakePointVisible and addMargins change the X and Y ranges to put the cursor fully in the view.

[NumWorksBot]

	.text	.rodata	.bss	.data
Base	636 612 bytes	230 451 bytes	174 968 bytes	216 bytes
Head	636 556 bytes	230 451 bytes	174 968 bytes	216 bytes
	- 56 bytes	+ 0 bytes	+ 0 bytes	+ 0 bytes
	- 0 %	+ 0 %	+ 0 %	+ 0 %

[NumWorksBot]

	.text	.rodata	.bss	.data
Base	636 612 bytes	230 451 bytes	174 968 bytes	216 bytes
Head	636 556 bytes	230 451 bytes	174 968 bytes	216 bytes
	- 56 bytes	+ 0 bytes	+ 0 bytes	+ 0 bytes
	- 0 %	+ 0 %	+ 0 %	+ 0 %