remove connection from pool if explicitly closed

src/db/connection.cr

@@ -38,6 +38,7 @@ module DB
     protected def do_close
       @statements_cache.each_value &.close
       @statements_cache.clear
+      @database.pool.delete self
     end
   end
 end

src/db/pool.cr

@@ -88,8 +88,7 @@ module DB
         rescue e : ConnectionLost
           # if the connection is lost close it to release resources
           # and remove it from the known pool.
-          @total.delete(e.connection)
+          delete(e.connection)
-          @available.delete(e.connection)
           e.connection.close
         end
       end
@@ -103,11 +102,17 @@ module DB
       end
     end
 
-    # :nodon:
+    # :nodoc:
     def is_available?(resource : T)
       @available.includes?(resource)
     end
 
+    # :nodoc:
+    def delete(resource : T)
+      @total.delete(resource)
+      @available.delete(resource)
+    end
+
     private def build_resource : T
       resource = @factory.call
       @total << resource