fix for possible cursor-related scren corruption

src/kernal/screen_m65/mega65_cursor.s

@@ -10,10 +10,28 @@
 // - GDCOL (colour under cursor)
 //
 
+
+m65_cursor_disable:       // XXX utilize this!
+
+	// Make sure IRQ won't interfere by increasing the counter      XXX reuse in legacy mode
+	lda #$FF
+	sta BLNCT
+
+	// Disable cursor blinking
+	lda #$80
+	sta BLNSW
+
+	// FALLTHROUGH
+
 m65_cursor_hide_if_visible:
 
+	// Set countdown to high value, to prevent IRQ interference
+	lda #$FF
+	sta BLNCT
+
+	// If cursor is not visible, nothing to do
 	lda BLNON
-	beq m65_cursor_end
+	beq m65_cursor_blink_timer_reset
 
 	// FALLTROUGH
 
@@ -21,8 +39,10 @@ m65_cursor_undraw:
 
 	// XXX provide implementation
 
-	lda #$80
-	sta BLNSW
+
+	// Mark cursor as not drawn
+	lda #0
+	sta BLNON
 
 	rts
 
@@ -35,6 +55,14 @@ m65_cursor_show_if_enabled:
 
 	// FALLTROUGH
 
-m65_cursor_end:
+m65_cursor_blink_timer_reset:    // XXX reuse code from main KERNAL
 
-	rts
+	// Rest blink counter (Mapping the 64, p39-40)
+	lda #20
+	sta BLNCT
+
+	// FALLTROUGH
+
+m65_cursor_blink_end:
+
+	rts