wayland: force monitor DPI to 96 when it’s unreasonably high

If an output has a bogus physical width or height, the DPI can become
so high that the cell width/height is too large for
pixman_image_fill_rectangles(), resulting in a crash in pixman_fill().

Since it doesn’t make any sense to use a DPI that is obviously bogus,
don’t. Force it 96 instead.

CHANGELOG.md

@@ -64,6 +64,7 @@
   ("permanently reset") instead of `2` ("reset") for DEC private
   modes that are known but unsupported.
 * Set `PWD` environment variable in the slave process ([#1179][1179]).
+* DPI is now forced to 96 when found to be unreasonably high.
 
 [1166]: https://codeberg.org/dnkl/foot/issues/1166
 [1179]: https://codeberg.org/dnkl/foot/issues/1179

wayland.c

@@ -409,6 +409,14 @@ output_update_ppi(struct monitor *mon)
 
     double px_diag = sqrt(pow(scaled_width, 2) + pow(scaled_height, 2));
     mon->dpi = px_diag / mon->inch * mon->scale;
+
+    if (mon->dpi > 1000) {
+        if (mon->name != NULL) {
+            LOG_WARN("%s: DPI=%f is unreasonable, using 96 instead",
+                     mon->name, mon->dpi);
+        }
+        mon->dpi = 96;
+    }
 }
 
 static void