Fix crash when manually drawing a hydrogen PR#679.

To reproduce the crash:
1) Draw something
2) Turn off adjust hydrogens and delete a hydrogen or another atom
3) Turn on adjust hydrogens again, set the element to hydrogen.
4) Draw from the atom to a new space (for the hydrogen).
5) Everything fine until mouseRelease. Crash.
Now we don't try to adjust hydrogens when drawing a hydrogen atom.

Change-Id: I4d5eaf6b596051a6c61a75e621c2693255adf8d8
Merge topic 'FIX_draw_hydrogen_crash' into master

43705c7e Fix crash when manually drawing a hydrogen PR#679.