hgview #84939 should fall back to the text interface if qt is not there [validation pending]

If the qt interface is not installed and the user didn't specify an interface on the command line or in their config, we should fall back to the text interface, not crash.

prioritynormal
typebug
done in1.5.0
load0.100
load left0.000
closed by#6257f4fa274b Fall back to the text interface if qt is not available (closes #84939)