Suggestion for some fixes

Trying to compile tvheadend with clang compiler i found some warnings.
ec780189d4c1f5b7630b16c5dfc6a8d1d820876e:
Substraction of two unsigned ints is always >=0. So the 'abs()' does not do what it was intended to do.

bdc545ba7a501c2f5f84afc102c820c08908d241:
I think, it was intended to compare the value of min/max duration. the address will always be != NULL.


f624d2eea1fbf6712e743517ee4be105344742d4
The enum was defined twice, with bad assignment between both types.
Use inline function for this short expression.