fix: write correct branchorder to net file (#335)

* #334 fix branchorder writing to net file

* autoformat: isort & black

Co-authored-by: xldeltares <xldeltares@users.noreply.github.com>

hydrolib/core/io/net/models.py

@@ -772,7 +772,9 @@ def _add_branch(
         self.branches[name] = branch
 
         # Add branch administration
-        self.network1d_branch_order = np.append(self.network1d_branch_order, -1)
+        self.network1d_branch_order = np.append(
+            self.network1d_branch_order, branch_order
+        )
         self.network1d_branch_length = np.append(
             self.network1d_branch_length, branch.length
         )