Fix PathRemoveRelativeParts for rooted paths

Source/Engine/Platform/Base/StringUtilsBase.cpp

@@ -261,7 +261,7 @@ void StringUtils::PathRemoveRelativeParts(String& path)
     path.Clear();
     for (auto& e : stack)
         path /= e;
-    if (isRooted)
+    if (isRooted && path[0] != '/')
         path.Insert(0, TEXT("/"));
 }
 

Source/Engine/Utilities/StringUtils.cs

@@ -227,7 +227,7 @@ namespace FlaxEngine
 
             bool isRooted = path.StartsWith("/");
             string result = string.Join(Path.DirectorySeparatorChar.ToString(), stack.Reverse());
-            if (isRooted)
+            if (isRooted && result[0] != '/')
                 result = result.Insert(0, "/");
             return result;
         }

Source/Tools/Flax.Build/Utilities/Utilities.cs

@@ -517,7 +517,7 @@ namespace Flax.Build
 
             bool isRooted = path.StartsWith("/");
             string result = string.Join(Path.DirectorySeparatorChar.ToString(), stack.Reverse());
-            if (isRooted)
+            if (isRooted && result[0] != '/')
                 result = result.Insert(0, "/");
             return result;
         }