Proper return value for ExecuteNonQuery according to "spec" (DNET-927).

Author: cincuranet

Provider/src/FirebirdSql.Data.FirebirdClient.Tests/FbCommandTests.cs

@@ -844,6 +844,17 @@ public void PassesDateTimeWithProperPrecision()
 			}
 		}
 
+		[Test]
+		public void ExecuteNonQueryReturnsMinusOneOnNonInsertUpdateDelete()
+		{
+			using (var cmd = Connection.CreateCommand())
+			{
+				cmd.CommandText = "select 1 from rdb$database";
+				var ra = cmd.ExecuteNonQuery();
+				Assert.AreEqual(-1, ra);
+			}
+		}
+
 		#endregion
 	}
 }

Provider/src/FirebirdSql.Data.FirebirdClient/FirebirdClient/FbCommand.cs

@@ -463,7 +463,13 @@ public override int ExecuteNonQuery()
 				throw;
 			}
 
-			return RecordsAffected;
+			return _statement.StatementType switch
+			{
+				DbStatementType.Insert => RecordsAffected,
+				DbStatementType.Update => RecordsAffected,
+				DbStatementType.Delete => RecordsAffected,
+				_ => -1,
+			};
 		}
 
 		public new FbDataReader ExecuteReader() => ExecuteReader(CommandBehavior.Default);