More honest error message in when failing to draw species.
More honest error message in when failing to draw species.

It used to assume the error was lack of molecular structure,
when in fact it could be anything.
nickvandewiele/RMG-Py,nickvandewiele/RMG-Py,pierrelb/RMG-Py,chatelak/RMG-Py,faribas/RMG-Py,KEHANG/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,pierrelb/RMG-Py,comocheng/RMG-Py