bugfix: Make sure symbol exists before calling owner

Author: tgodzik

compiler/src/dotty/tools/dotc/semanticdb/ExtractSemanticDB.scala

@@ -190,7 +190,7 @@ class ExtractSemanticDB extends Phase:
                 registerUseGuarded(None, privateWithin, spanOfSymbol(privateWithin, tree.span, tree.source), tree.source)
             else if !excludeSymbol(tree.symbol) then
               registerSymbol(tree.symbol, symbolKinds(tree))
-        case tree: Template if tree.symbol.owner.is(Invisible) =>
+        case tree: Template if tree.symbol != NoSymbol && tree.symbol.owner.is(Invisible) =>
           // do nothing
           // exclude the symbols and synthetics generated by @main annotation
           // (main class generated by @main has `Invisible` flag, see `MainProxies.scala`).
@@ -201,7 +201,7 @@ class ExtractSemanticDB extends Phase:
           val selfSpan = tree.self.span
           if selfSpan.exists && selfSpan.hasLength then
             traverse(tree.self)
-          if tree.symbol.owner.isEnumClass then
+          if tree.symbol != NoSymbol && tree.symbol.owner.isEnumClass then
             tree.body.foreachUntilImport(traverse).foreach(traverse) // the first import statement
           else
             tree.body.foreach(traverse)