Add DBD::Mock::Session->current_state method

This just makes the code simpler to follow. Particularly the portion
in validate_bound_params where results are loaded into the $tracker
object.

lib/DBD/Mock.pm

@@ -622,9 +622,12 @@ sub execute {
 
     if (my $session = $dbh->{mock_session}) {
         eval {
+            my $state = $session->current_state;
             $session->verify_bound_params($dbh, $tracker->bound_params());
-            my $idx = $session->{state_index} - 1;
-            my @results = @{$session->{states}->[$idx]->{results}};
+
+            # Load a copy of the results to return (minus the field
+            # names) into the tracker
+            my @results = @{$state->{results}};
             shift @results;
             $tracker->{return_data} = \@results;
         };
@@ -1193,6 +1196,12 @@ sub name  { (shift)->{name} }
 sub reset { (shift)->{state_index} = 0 }
 sub num_states { scalar( @{ (shift)->{states} } ) }
 
+sub current_state {
+    my $self = shift;
+    my $idx = $self->{state_index};
+    return $self->{states}[$idx];
+}
+
 sub has_states_left {
     my $self = shift;
     return $self->{state_index} < scalar(@{$self->{states}});
@@ -1204,7 +1213,7 @@ sub verify_statement {
     ($self->has_states_left)
         || die "Session states exhausted, only '" . scalar(@{$self->{states}}) . "' in DBD::Mock::Session (" . $self->{name} . ")";
 
-    my $current_state = $self->{states}->[$self->{state_index}];
+    my $current_state = $self->current_state;
     # make sure our state is good
     (exists ${$current_state}{statement} && exists ${$current_state}{results})
         || die "Bad state '" . $self->{state_index} .  "' in DBD::Mock::Session (" . $self->{name} . ")";
@@ -1236,7 +1245,8 @@ sub verify_statement {
 
 sub verify_bound_params {
     my ($self, $dbh, $params) = @_;
-    my $current_state = $self->{states}->[$self->{state_index}];
+
+    my $current_state = $self->current_state;
     if (exists ${$current_state}{bound_params}) {
         my $expected = $current_state->{bound_params};
         (scalar(@{$expected}) == scalar(@{$params}))