DECRQCRA: treat uninitialized cells as spaces

The concept of uninitialized cells in wezterm is not the same as that on
VT520 or that on xterm, so treat them as spaces, at least when asking
for the checksum of a single cell, which is what esctest does.

term/src/terminalstate/mod.rs

@@ -1979,7 +1979,17 @@ impl TerminalState {
                 checksum += u16::from(ch as u8);
             }
         }
-        checksum
+
+        // Treat uninitialized cells as spaces.
+        // The concept of uninitialized cells in wezterm is not the same as that on VT520 or that
+        // on xterm, so, to prevent a lot of noise in esctest, treat them as spaces, at least when
+        // asking for the checksum of a single cell (which is what esctest does).
+        // See: https://github.com/wez/wezterm/pull/4565
+        if checksum == 0 {
+            32u16
+        } else {
+            checksum
+        }
     }
 
     fn perform_csi_window(&mut self, window: Window) {