scripts: csv.py: Fixed divide by zero in ratio

This now returns 1.0 if the total part of the fraction is 0.

There may be a better way to handle this, but the intention is for 0/0
to map to 100% for thing like code coverage (cov.py), test coverage
(test.py), etc.

scripts/csv.py

@@ -597,7 +597,10 @@ class RExpr:
 
         def eval(self, fields={}):
             v = self.a.eval(fields)
-            return RFloat(float(v.a) / float(v.b))
+            if not float(v.b):
+                return RFloat(1)
+            else:
+                return RFloat(float(v.a) / float(v.b))
 
     @func('total')
     class Total(Expr):