Fix: Crash when clearing the start pressure field in cylinder picker (#188)

Author: Rolf-Smit

composeApp/src/commonMain/kotlin/org/neotech/app/abysner/presentation/screens/planner/cylinders/CylinderPickerBottomSheet.kt

@@ -280,7 +280,9 @@ private fun CylinderPickerBottomSheetContent(
                     visualTransformation = SuffixVisualTransformation(" ${unitSystem.pressureUnitLabel}"),
                     errorMessage = errorMessagePressure,
                     onNumberChanged = {
-                        startPressure = it
+                        if (it != null) {
+                            startPressure = it
+                        }
                     },
                     supportingText = null
                 )