[SourceKit] Ignore references without a location

A keypath using dynamic member lookup results in various `KeyPathExpr`
that have components with no location. Ignore these and any other
references that have a missing location.

Resolves rdar://85237365

tools/SourceKit/lib/SwiftLang/SwiftDocSupport.cpp

@@ -1143,7 +1143,7 @@ public:
   bool visitDeclReference(ValueDecl *D, CharSourceRange Range,
                           TypeDecl *CtorTyRef, ExtensionDecl *ExtTyRef, Type Ty,
                           ReferenceMetaData Data) override {
-    if (Data.isImplicit)
+    if (Data.isImplicit || !Range.isValid())
       return true;
     unsigned StartOffset = getOffset(Range.getStart());
     References.emplace_back(D, StartOffset, Range.getByteLength(), Ty);