Fix Findsodium.cmake version test.

cmake/Findsodium.cmake

@@ -213,12 +213,12 @@ endif()
 
 # extract sodium version
 if (sodium_INCLUDE_DIR)
-    set(_VERSION_HEADER "${_INCLUDE_DIR}/sodium/version.h")
-    if (EXISTS _VERSION_HEADER)
+    set(_VERSION_HEADER "${sodium_INCLUDE_DIR}/sodium/version.h")
+    if (EXISTS "${_VERSION_HEADER}")
         file(READ "${_VERSION_HEADER}" _VERSION_HEADER_CONTENT)
         string(REGEX REPLACE ".*#[ \t]*define[ \t]*SODIUM_VERSION_STRING[ \t]*\"([^\n]*)\".*" "\\1"
             sodium_VERSION "${_VERSION_HEADER_CONTENT}")
-        set(sodium_VERSION "${sodium_VERSION}" PARENT_SCOPE)
+        set(sodium_VERSION "${sodium_VERSION}")
     endif()
 endif()