rgbmatrix: validate width= constructor parameter

In adafruit#3482, @cwalther noted that, hypothetically, a zero byte allocation
could be made in the RGBMatrix constructor.  Ensure that width is positive.
Height was already checked against the number of RGB pins if it was specified,
so zero is ruled out there as well.

Author: jepler

shared-bindings/rgbmatrix/RGBMatrix.c

@@ -210,6 +210,10 @@ STATIC mp_obj_t rgbmatrix_rgbmatrix_make_new(const mp_obj_type_t *type, size_t n
         }
     }
 
+    if (args[ARG_width] <= 0) {
+        mp_raise_ValueError(translate("width must be greater than zero"));
+    }
+
     preflight_pins_or_throw(clock_pin, rgb_pins, rgb_count, true);
 
     mp_obj_t framebuffer = args[ARG_framebuffer].u_obj;