Fix OpenThreads install on MSVC without a prefix

All this change does is make the install config for OpenThreads identical to the one in ModuleInstall.cmake

src/OpenThreads/win32/CMakeLists.txt

@@ -59,6 +59,9 @@ INSTALL(
 
 IF(MSVC AND DYNAMIC_OPENSCENEGRAPH)
     GET_TARGET_PROPERTY(PREFIX ${LIB_NAME} PREFIX)
+    IF("${PREFIX}" STREQUAL PREFIX-NOTFOUND) # Fix for PREFIX-NOTFOUND left in file names
+	SET(PREFIX "")
+    ENDIF()
     IF( ${CMAKE_GENERATOR} STREQUAL "Ninja" )
 	INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/${PREFIX}${LIB_NAME}${CMAKE_RELEASE_POSTFIX}.pdb DESTINATION ${INSTALL_BINDIR} COMPONENT libopenthreads CONFIGURATIONS Release)
 	INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/${PREFIX}${LIB_NAME}${CMAKE_RELWITHDEBINFO_POSTFIX}.pdb DESTINATION ${INSTALL_BINDIR} COMPONENT libopenthreads CONFIGURATIONS RelWithDebInfo)