py,st3m: Touchable: Don't report current gesture when the state is UP

Also, don't report ENDED state if the gesture never actually started.
Fixes a crash in CapScrollController, observable in Files and Scroll Demo
by quickly tapping the petal as the first interaction.

python_payload/st3m/input.py

@@ -405,8 +405,9 @@ class Touchable:
         self._pressed = petal.pressed
 
         if not self._pressed:
-            if not self._prev_pressed:
+            if not self._prev_pressed or self._start is None:
                 self._state = self.UP
+                self._start = None
             else:
                 self._state = self.ENDED
             return