Fix T49323: Ineffective bone roll calculation with low rig scale

The code was expecting vector to be normalized, however after
applying inverted object matrix it was possible to have scale
applied to it.

source/blender/editors/armature/armature_edit.c

@@ -410,6 +410,7 @@ static int armature_calc_roll_exec(bContext *C, wmOperator *op)
 			if (type < 3) vec[type] = 1.0f;
 			else vec[type - 2] = -1.0f;
 			mul_m3_v3(imat, vec);
+			normalize_v3(vec);
 		}
 		
 		if (axis_flip) negate_v3(vec);