Bug ILI932x: negative X1 coordinate

ILI9325/8: When values 1 or 3 are passed to function setRotation(), the function setAddrWindow() will produce [negative X1 coordinate](https://github.com/adafruit/TFTLCD-Library/blob/master/Adafruit_TFTLCD.cpp#L396).
Solution: [check y2 value before updating x1](https://github.com/stevstrong/TFTLCD-Library/commit/a85f16b8965908bbdb9d41493ef4dbf44025579f)
**EDIT**
I just updated the links and the name of the issue (sorry, I am newbie in handling github functions :) )

Start in Adafruit_TFTLCD.cpp at setAddrWindow(), then trace how setRotation() values 1 and 3 affect it. Reproduce those rotations and verify that checking y2 before updating x1 prevents a negative X1 coordinate, using the linked commit as the reference for done.

Written by the indexing model from the issue text.