While generating Java JNI wrappers package names with an underscore (`_`) character where not properly escaped according to https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/design.html#resolving_native_method_names (see also: https://github.com/Itseez/opencv_contrib/issues/652).

This fix replaces all the occurrences of `_` with `_1` resulting in proper JNI method names.