src: fix potential segmentation fault in SQLite

The Local<Value> returned from ColumnToValue() and ColumnNameToValue()
may be empty (if a JavaScript exception is pending), in which case a
segmentation fault may occur at the call sites, which do not check if
the Local<Value> is empty. Fix this bug returning early if an exception
is pending (as indicated by the Local being empty).

In the long term, these functions should return MaybeLocal instead of
Local, but this patch is supposed to be a minimal bug fix only.

src/node_sqlite.cc

@@ -441,7 +441,9 @@ void StatementSync::All(const FunctionCallbackInfo<Value>& args) {
 
     for (int i = 0; i < num_cols; ++i) {
       Local<Value> key = stmt->ColumnNameToValue(i);
+      if (key.IsEmpty()) return;
       Local<Value> val = stmt->ColumnToValue(i);
+      if (val.IsEmpty()) return;
 
       if (row->Set(env->context(), key, val).IsNothing()) {
         return;
@@ -483,7 +485,9 @@ void StatementSync::Get(const FunctionCallbackInfo<Value>& args) {
 
   for (int i = 0; i < num_cols; ++i) {
     Local<Value> key = stmt->ColumnNameToValue(i);
+    if (key.IsEmpty()) return;
     Local<Value> val = stmt->ColumnToValue(i);
+    if (val.IsEmpty()) return;
 
     if (result->Set(env->context(), key, val).IsNothing()) {
       return;