[#107] Fixed check for empty submodule directory

Signed-off-by: Tobias Frisch <tfrisch@uni-koblenz.de>

config/ext/Git.cmake

@@ -38,7 +38,9 @@ function(init_git_submodules)
 endfunction()
 
 function(use_git_submodule submodule_path submodule_status)
-    if (EXISTS "${submodule_path}")
+    file(GLOB path_glob "${submodule_path}")
+    list(LENGTH path_glob glob_len)
+    if(glob_len GREATER 0)
         set(${submodule_status} TRUE PARENT_SCOPE)
         return()
     endif()
@@ -57,7 +59,9 @@ function(use_git_submodule submodule_path submodule_status)
                 COMMENT "Updating Git Submodules"
         )
 
-        if (EXISTS "${submodule_path}")
+        file(GLOB path_glob "${submodule_path}")
+        list(LENGTH path_glob glob_len)
+        if(glob_len GREATER 0)
             set(${submodule_status} TRUE PARENT_SCOPE)
             return()
         endif()