Slap Melee Hardening on the rifle and you have a durable rifle. With that, I would remove the additional penalties associated for melee combat. Otherwise, unless mentioned in the description, I don't believe any of the rifles in Arsenal are exempt from the Edge Test.
Edit: Alternatively, I'd allow a modified Melee Hardening modification to give the same benefits that the Walther has, with the same drawback.
Bug--I think TeaTime is referring to:
QUOTE (SR4A @ p. 319)
At the end of every Turn in which the rifle is
used in a running firefight (as opposed to a sniping situation), roll an
Edge Test. For every Edge Test failed, the weapon incurs a –1 dice
pool modifier until it is recalibrated with an Armorer + Logic (8, 1
Minute) Extended Test. The modifier is doubled if the weapon is used
in combat as a melee weapon or to defend from a melee attack.