Ensure PythonLibsNew_FOUND is set in FindPythonLibsNew module (#1373)

Since the module is named FindPythonLibsNew, PythonLibsNew_FOUND should be set appropriately.
diff --git a/tools/FindPythonLibsNew.cmake b/tools/FindPythonLibsNew.cmake
index 919a384..7d85af4 100644
--- a/tools/FindPythonLibsNew.cmake
+++ b/tools/FindPythonLibsNew.cmake
@@ -64,6 +64,7 @@
 
 if(NOT PYTHONINTERP_FOUND)
     set(PYTHONLIBS_FOUND FALSE)
+    set(PythonLibsNew_FOUND FALSE)
     return()
 endif()
 
@@ -96,6 +97,7 @@
             "Python config failure:\n${_PYTHON_ERROR_VALUE}")
     endif()
     set(PYTHONLIBS_FOUND FALSE)
+    set(PythonLibsNew_FOUND FALSE)
     return()
 endif()
 
@@ -127,6 +129,7 @@
             "chosen compiler is  ${_CMAKE_BITS}-bit")
     endif()
     set(PYTHONLIBS_FOUND FALSE)
+    set(PythonLibsNew_FOUND FALSE)
     return()
 endif()
 
@@ -196,3 +199,4 @@
     "${PYTHON_EXECUTABLE}${PYTHON_VERSION}")
 
 set(PYTHONLIBS_FOUND TRUE)
+set(PythonLibsNew_FOUND TRUE)