cmake: fix FindJava/FindJNI wrappers for cmake re-runs

when cmake is re-run and include(FindJAVA) is skipped,
JAVA_FOUND should still be set. Same for JNI.

cmake/FindJNI.cmake

+if(JAVA_AWT_LIBRARY)
+  set(JNI_FOUND TRUE)
+  return()
+endif()
 if(DEFINED JAVA_AWT_LIBRARY)
+  set(JNI_FOUND FALSE)
   return()
 endif()
 

cmake/FindJava.cmake

+if(Java_JAVA_EXECUTABLE)
+  set(JAVA_FOUND TRUE)
+  return()
+endif()
 if(DEFINED Java_JAVA_EXECUTABLE)
+  set(JAVA_FOUND FALSE)
   return()
 endif()