Refactor coercion predicate function to make it clearer what happens for the...

Refactor coercion predicate function to make it clearer what happens for the template based conversions and for the non-template string conversions.

Cython/Compiler/PyrexTypes.py

@@ -3424,13 +3424,17 @@ class CppClassType(CType):
             return ''
 
     def can_coerce_from_pyobject(self, env):
-        if self.cname in builtin_cpp_conversions or self.cname in cpp_string_conversions:
+        if self.cname in builtin_cpp_conversions:
+            template_count = builtin_cpp_conversions[self.cname]
             for ix, T in enumerate(self.templates or []):
-                if ix >= builtin_cpp_conversions[self.cname]:
+                if ix >= template_count:
                     break
                 if T.is_pyobject or not T.can_coerce_from_pyobject(env):
                     return False
             return True
+        elif self.cname in cpp_string_conversions:
+            return True
+        return False
 
     def create_from_py_utility_code(self, env):
         if self.from_py_function is not None: