Fix out-of-bounds textures in [combine

[OgelGames]

Fixes #24 by preventing character and fill textures from being added past the end of each line of text.

[Niklp09]

Works, I prefer this over #25.

[appgurueu]

Why? I'm not convinced keeping the fill_line hack is a good idea; I don't see why it would be needed for the signs_lib functionality, and it surely is inefficient.

To me, the other PR cuts down on the mess and dirty hacks, while this PR adds further complexity. Assuming both ultimately implement the same features correctly, why prefer this PR?

I'd also be interested in hearing what @tenplus1 thinks.

[tenplus1]

@appgurueu is corrent, while this may work it adds further complexity and sticks with the old masking method of sign creation that was hacky to begin with. The updated method in #25 only has to draw the coloured text itself which results in faster creation of signage.

[OgelGames]

Neither method is significantly better or worse than the other, and it's definitely not a hack to use masking to color the text.

The biggest difference is that this PR fixes the cause of the out-of-bounds textures, preventing overflowing text from being added to the texture.

[OgelGames]

It's been 2 weeks, merging this.