row_offsets

[ghost]

Corrected 'row_offsets' for LCDs with 4 lines.

[mathertel]

This is a picture of another 4-row LCD that has 20 columns each row. Here the original values fit.
Here the offset for the 3. line offset = 1 line offset + 20.

Your display has 16 cols per row and need the adjustment 3. line offset = 1 line offset + 16.

The cols actually are known from the begin() function but not yet used. They can be used to calculate the offset array properly.
row_offsets[2] = row_offsets[0] + cols; row_offsets[3] = row_offsets[1] + cols.
You ma ylike to add this to your pull request.
Thanks for pointing to that incompatibility with 4 lines-16 cols displays..

[ghost]

I created a new function for preparing row_offsets at begin(), then setCursor() may faster change the cursor position. Please review changes.

[mathertel]

Thanks a lot.

[mathertel]

While doing some quality checks I found a simpler way of initializing.
The row_offsets can always be initialized for max 4 rows. In a 2*16 case only 2 of them are actually used.
Added some boundary checks as well.