Fix fallback speed validity checks (#5300)

* fix fallback_speeds check to only accept values > 0

* add invalid_fallback_speed

src/engine/plugins/table.cpp

@@ -96,7 +96,7 @@ Status TablePlugin::HandleRequest(const RoutingAlgorithmsInterface &algorithms,
     }
 
     // Scan table for null results - if any exist, replace with distance estimates
-    if (params.fallback_speed > 0 || params.scale_factor > 0)
+    if (params.fallback_speed != INVALID_FALLBACK_SPEED || params.scale_factor > 0)
     {
         for (std::size_t row = 0; row < num_sources; row++)
         {
@@ -104,7 +104,7 @@ Status TablePlugin::HandleRequest(const RoutingAlgorithmsInterface &algorithms,
             {
                 const auto &table_index = row * num_destinations + column;
                 BOOST_ASSERT(table_index < result_tables_pair.first.size());
-                if (params.fallback_speed > 0 &&
+                if (params.fallback_speed != INVALID_FALLBACK_SPEED && params.fallback_speed > 0 &&
                     result_tables_pair.first[table_index] == MAXIMAL_EDGE_DURATION)
                 {
                     const auto &source =

src/server/service/table_service.cpp

@@ -56,7 +56,7 @@ std::string getWrongOptionHelp(const engine::api::TableParameters &parameters)
         help = "Number of coordinates needs to be at least two.";
     }
 
-    if (parameters.fallback_speed < 0)
+    if (parameters.fallback_speed <= 0)
     {
         help = "fallback_speed must be > 0";
     }