Shell: Don't crash when autocompleting a non-bare word

For example, type 'Hello?' without the quotation marks but with the
question mark, and press TAB.

Previously, this would crash the Shell. Now, it merely refuses
to make any suggestions.

We could do better, but that is too hard for now.

Shell/AST.cpp

@@ -441,10 +441,9 @@ HitTestResult CastToCommand::hit_test_position(size_t offset)
 Vector<Line::CompletionSuggestion> CastToCommand::complete_for_editor(Shell& shell, size_t offset, const HitTestResult& hit_test_result)
 {
     auto matching_node = hit_test_result.matching_node;
-    if (!matching_node)
+    if (!matching_node || !matching_node->is_bareword())
         return {};
 
-    ASSERT(matching_node->is_bareword());
     auto corrected_offset = offset - matching_node->position().start_offset;
     auto* node = static_cast<BarewordLiteral*>(matching_node.ptr());
 
@@ -953,10 +952,9 @@ HitTestResult Execute::hit_test_position(size_t offset)
 Vector<Line::CompletionSuggestion> Execute::complete_for_editor(Shell& shell, size_t offset, const HitTestResult& hit_test_result)
 {
     auto matching_node = hit_test_result.matching_node;
-    if (!matching_node)
+    if (!matching_node || !matching_node->is_bareword())
         return {};
 
-    ASSERT(matching_node->is_bareword());
     auto corrected_offset = offset - matching_node->position().start_offset;
     auto* node = static_cast<BarewordLiteral*>(matching_node.ptr());
 
@@ -1204,10 +1202,9 @@ HitTestResult PathRedirectionNode::hit_test_position(size_t offset)
 Vector<Line::CompletionSuggestion> PathRedirectionNode::complete_for_editor(Shell& shell, size_t offset, const HitTestResult& hit_test_result)
 {
     auto matching_node = hit_test_result.matching_node;
-    if (!matching_node)
+    if (!matching_node || !matching_node->is_bareword())
         return {};
 
-    ASSERT(matching_node->is_bareword());
     auto corrected_offset = offset - matching_node->position().start_offset;
     auto* node = static_cast<BarewordLiteral*>(matching_node.ptr());