Deal with unexpected ResultSet#read types during runtime.

spec/custom_drivers_types_spec.cr

@@ -197,7 +197,7 @@ describe DB do
         FooDriver.fake_row = [1] of FooDriver::Any
         db.query "query" do |rs|
           rs.move_next
-          expect_raises(TypeCastError) do
+          expect_raises(Exception, "FooResultSet#read returned a Int32. A BarValue was expected.") do
             w.check
             rs.read(BarValue)
           end
@@ -210,7 +210,7 @@ describe DB do
         BarDriver.fake_row = [1] of BarDriver::Any
         db.query "query" do |rs|
           rs.move_next
-          expect_raises(TypeCastError) do
+          expect_raises(Exception, "BarResultSet#read returned a Int32. A FooValue was expected.") do
             w.check
             rs.read(FooValue)
           end

src/db/result_set.cr

@@ -76,7 +76,12 @@ module DB
 
     # Reads the next column value as a **type**
     def read(type : T.class) : T forall T
-      read.as(T)
+      value = read
+      if value.is_a?(T)
+        value
+      else
+        raise "#{self.class}#read returned a #{value.class}. A #{T} was expected."
+      end
     end
 
     # Reads the next columns and returns a tuple of the values.