AP_Terrain: add init_failed

allows external caller to determine if terrain database failed to initialise

libraries/AP_Terrain/AP_Terrain.cpp

@@ -386,9 +386,11 @@ bool AP_Terrain::allocate(void)
     if (cache == nullptr) {
         enable.set(0);
         gcs().send_text(MAV_SEVERITY_CRITICAL, "Terrain: Allocation failed");
+        memory_alloc_failed = true;
         return false;
     }
     cache_size = TERRAIN_GRID_BLOCK_CACHE_SIZE;
+    memory_alloc_failed = false;
     return true;
 }
 

libraries/AP_Terrain/AP_Terrain.h

@@ -179,6 +179,11 @@ public:
      */
     void get_statistics(uint16_t &pending, uint16_t &loaded) const;
 
+    /*
+      returns true if initialisation failed because out-of-memory
+     */
+    bool init_failed() const { return memory_alloc_failed; }
+
 private:
     // allocate the terrain subsystem data
     bool allocate(void);
@@ -414,6 +419,9 @@ private:
     // status
     enum TerrainStatus system_status = TerrainStatusDisabled;
 
+    // memory allocation status
+    bool memory_alloc_failed;
+
     static AP_Terrain *singleton;
 };
 #endif // AP_TERRAIN_AVAILABLE