report not finding a template correctly

TtRenderer was dying with a 'not found' error when a template was not
found, instead of returning 0, which was interfering with things like
the error screen.

Use $provider->fetch to find templates and return 0 when a template is
not found.

lib/Mojolicious/Plugin/TtRenderer/Engine.pm

@@ -12,6 +12,7 @@ use Mojo::ByteStream 'b';
 use Template ();
 use Cwd qw/abs_path/;
 use Scalar::Util 'weaken';
+use POSIX ':errno_h';
 
 __PACKAGE__->attr('tt');
 
@@ -87,11 +88,26 @@ sub _render {
     my $provider = $self->tt->{SERVICE}->{CONTEXT}->{LOAD_TEMPLATES}->[0];
     $provider->options($options);
     $provider->ctx($c);
-    $provider->not_found(0);
 
-    my $ok = $self->tt->process(defined $inline ? \$inline : $t, @params);
+    my $ok = do {
+        if (defined $inline) {
+            $self->tt->process(\$inline, @params);
+        }
+        else {
+            my @ret = $provider->fetch($t);
 
-    return 0 if $provider->not_found;
+            if (not defined $ret[1]) {
+                $self->tt->process($ret[0], @params);
+            }
+            elsif (not defined $ret[0]) { # not found
+                return 0;
+            }
+            else { # error
+                return 0 if $! == ENOENT && (not ref $ret[0]); # not found when not blessed exception
+                die $ret[0];
+            }
+        }
+    };
 
     # Error
     die $self->tt->error unless $ok;