Gui: Don't use this pointer after valueChanged in EditableDatumLabel

Simple fix for such a simple error I didn't see. Basically,
`valueChanged` signal can result in EditableDatumLabel being deleted
(for example, when we are on the last OVP and all of the OVPs have been
accepted). This could result in crashes as reported in previous issues,
because just after emitting this signal we were trying to use `this` pointer,
which wasn't available anymore as we deleted EditableDatumLabel obj that
was attached to it, so in essence we were dereferencing some random
address.

Fix for that is simple - move the check for `hasFinishedEditing` flag to
check locked appearance in `validateAndFinish` lambda, as it already
does validation and this way we will avoid referencing internals (which
could be deallocated) after emitting this signal.

src/Gui/EditableDatumLabel.cpp

@@ -205,6 +205,11 @@ void EditableDatumLabel::startEdit(double val, QObject* eventFilteringObj, bool
         value = spinBox->rawValue();
 
         isSet = true;
+
+        if (this->hasFinishedEditing) {
+            this->setLockedAppearance(true);
+        }
+
         Q_EMIT this->valueChanged(value);
     };
 
@@ -237,12 +242,6 @@ bool EditableDatumLabel::eventFilter(QObject* watched, QEvent* event)
                     // regular enter
                     this->hasFinishedEditing = true;
                     Q_EMIT this->spinBox->valueChanged(this->value);
-
-                    // only set lock state if it passed validation
-                    // (validation can unset isSet if value didn't pass
-                    // confusion point for example)
-                    if (this->isSet)
-                        this->setLockedAppearance(true);
                     return true;
                 }
             }