Fix issue with finding assimp on consecutive cmake runs

3rdParty/assimp/CMakeLists.txt

@@ -1,5 +1,6 @@
 include(FetchContent)
 
+unset(assimp_FOUND)
 find_package(assimp QUIET)
 if (assimp_FOUND)
     message("Using system assimp")
@@ -25,15 +26,15 @@ elseif (USE_ASSIMP)
 
     FetchContent_MakeAvailable(assimp)
 
-    set(assimp_FOUND "fetched assimp found" CACHE INTERNAL ON)
+    set(assimp_BUILT "fetched assimp found" CACHE INTERNAL ON)
 endif ()
 
 
 function(LinkAssimp TARGET)
-    if (NOT assimp_FOUND)
+    if (NOT assimp_BUILT)
         find_package(assimp QUIET)
     endif ()
-    if (assimp_FOUND)
+    if (assimp_FOUND OR assimp_BUILT)
         target_link_libraries(${TARGET} PUBLIC assimp)
     endif ()
 endfunction()