Workaround: No longer crashes during optimization with symmetry when "Atoms do not fit space group"

Random structure generation routine (where error was occurring) now returns false on this error to indicate that structure generation failed. At which point, the GA attempts to create a new random structure.

Work left to do:

1) Diagnose why this error was happening in the first space
2) Allow other structure generation errors to "return false" to be more consistent