Add SL3OpenFailedException

FossilOrigin-Name: 26a83e91f0807f2af6b7b95b33482e55c12ddd3365db835ed7d05e68738a399f

src/exceptions/SL3Exception.m

@@ -25,6 +25,11 @@
 @implementation SL3Exception
 @synthesize connection = _connection, errorCode = _errorCode;
 
++ (instancetype)exception
+{
+	OF_UNRECOGNIZED_SELECTOR
+}
+
 + (instancetype)exceptionWithConnection: (SL3Connection *)connection
 			      errorCode: (int)errorCode
 {
@@ -32,6 +37,11 @@
 				       errorCode: errorCode] autorelease];
 }
 
+- (instancetype)init
+{
+	OF_INVALID_INIT_METHOD
+}
+
 - (instancetype)initWithConnection: (SL3Connection *)connection
 			 errorCode: (int)errorCode
 {