[debugger] Ensure at least one breakable position per function.

src/interpreter/source-position-table.cc

Index: src/interpreter/source-position-table.cc
diff --git a/src/interpreter/source-position-table.cc b/src/interpreter/source-position-table.cc
index 1d7f368242d679501d5301e7e895b6585eaa0c52..5d30f51be7ff032111dd893d2e27f3463a1a0956 100644
--- a/src/interpreter/source-position-table.cc
+++ b/src/interpreter/source-position-table.cc
@@ -151,9 +151,10 @@ void SourcePositionTableBuilder::AddEntry(const PositionTableEntry& entry) {
 }
 
 Handle<ByteArray> SourcePositionTableBuilder::ToSourcePositionTable() {
+  if (bytes_.empty()) return isolate_->factory()->empty_byte_array();
+
   Handle<ByteArray> table = isolate_->factory()->NewByteArray(
       static_cast<int>(bytes_.size()), TENURED);
-  if (bytes_.empty()) return table;
 
   MemCopy(table->GetDataStartAddress(), &*bytes_.begin(), bytes_.size());