Make exception throwing consistent in the PDB gathering API. Avoid returning an empty symbol_table name when the PDB cannot be downloaded.

volatility3/framework/plugins/windows/netstat.py

@@ -649,10 +649,6 @@ class NetStat(interfaces.plugins.PluginInterface, timeliner.TimeLinerInterface):
             vollog.error("Unable to locate symbols for the memory image's tcpip module")
             return
 
-        if not tcpip_symbol_table:
-            vollog.error("Unable to reconstruct symbol table for tcpip.sys")
-            return
-
         for netw_obj in self.list_sockets(
             self.context,
             kernel.layer_name,

volatility3/framework/symbols/windows/pdbutil.py

@@ -409,6 +409,10 @@ class PDBUtility(interfaces.configuration.VersionableInterface):
         _, symbol_table_name = cls._modtable_from_pdb(
             context, config_path, layer_name, pdb_name, module_offset, module_size
         )
+
+        if symbol_table_name is None:
+            raise exceptions.VolatilityException(f"Symbol table could not be reconstructed for module {pdb_name}")
+
         return symbol_table_name
 
     @classmethod