Assembly: Fix infinite loop with subassembly. Fix #19319 (#22685)

* Assembly: Fix infinite loop with subassembly. Fix #19319

* squash

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update AssemblyObject.h

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/Mod/Assembly/Gui/ViewProviderAssembly.cpp

@@ -763,6 +763,8 @@ ViewProviderAssembly::DragMode ViewProviderAssembly::findDragMode()
             // If fixed joint we need to find the upstream joint to find move mode.
             // For example : Gnd -(revolute)- A -(fixed)- B : if user try to move B, then we should
             // actually move A
+            movingJoint = nullptr;  // reinitialize because getUpstreamMovingPart will call
+            // getJointOfPartConnectingToGround again which will find the same joint.
             auto* upPart =
                 assemblyPart->getUpstreamMovingPart(docsToMove[0].obj, movingJoint, pName);
             if (!movingJoint) {