Xray Filter thickness value of 0.00 recorded as None

[Ed McDonagh]

Should record value as presented

[Ed McDonagh]

Now checks for thickmin and thickmax being not None so 0.0 can be recorded. Refs #450 and should fix it be needs testing.

→ <<cset e536e1eb20f9>>

[Ed McDonagh]

Added 0.00 filter thickness fix to changes. Fixes #450

→ <<cset 574691baeb23>>

[Ed McDonagh]

Adding refs #431, #450 to changes. Fixes #431 again.

→ <<cset 0c8a136149bc>>