Disable the "synchronize from qfield button" if the wrong project (or no project) is open in QGIS

[gioman]

In the docs you clearly state "When you want to synchronize what you have collected, re-open the project in QGIS (the one you saved with a regular Save As)", but a user could start start "synchronize from qfield button" having opened the offline version of the project or no project at all. In this cases the original project is lost: if the offline project was open at the time of "synchronize from qfield button" the original project is overwritten with the offline one, if no project is open then the original project becomes empty.