Guard against negative coordinates (#4)

* Guard against negative coordinates

Closes #3

* Changelog entry

* Capital letter

Author: jamwaffles

CHANGELOG.md

@@ -8,6 +8,10 @@ projects using an SPI interface.
 
 ## [Unreleased] - ReleaseDate
 
+### Fixed
+
+- [#4](https://github.com/jamwaffles/ssd1331/pull/4) Guard against negative pixel coordinates panicking `draw_pixel()` calls.
+
 ## [0.2.0-alpha.2]
 
 ### Changed

src/display.rs

@@ -372,6 +372,12 @@ where
     fn draw_pixel(&mut self, pixel: drawable::Pixel<Rgb565>) {
         let drawable::Pixel(pos, color) = pixel;
 
+        // Guard against negative values. All positive i32 values from `pos` can be represented in
+        // the `u32`s that `set_pixel()` accepts.
+        if pos.x < 0 || pos.y < 0 {
+            return;
+        }
+
         self.set_pixel(
             (pos.x).try_into().unwrap(),
             (pos.y).try_into().unwrap(),