Catch C++ exceptions by const reference

Fixes #2277

libraries/classparser/src/classparser.cpp

@@ -70,9 +70,7 @@ QString GetMinecraftJarVersion(QString jarName)
 			}
 		}
 	}
-	catch (java::classfile_exception &)
-	{
-	}
+	catch (java::classfile_exception) { }
 
 	// clean up
 	delete[] classfile;

libraries/pack200/anti200.cpp

@@ -32,7 +32,7 @@ int main(int argc, char **argv)
 	{
 		unpack_200(input, output);
 	}
-	catch (std::runtime_error &e)
+	catch (const std::runtime_error &e)
 	{
 		std::cerr << "Bad things happened: " << e.what() << std::endl;
 		fclose(input);