WS30: Reduce log spam

Previously blank lines in the various .txt LIST files
created spurious error logging.  This commit does some
simple length checking and ignore blank lines rather than
complaining (and then ignoring).

simgear/scene/tgdb/AreaFeatureBin.cxx

@@ -58,6 +58,8 @@ AreaFeatureBin::AreaFeatureBin(const SGPath& absoluteFileName, const std::string
         std::string line;
         std::getline(stream, line);
 
+        if (line.length() == 0) continue;
+
         // strip comments
         std::string::size_type hash_pos = line.find('#');
         if (hash_pos != std::string::npos)

simgear/scene/tgdb/CoastlineBin.cxx

@@ -62,6 +62,8 @@ CoastlineBin::CoastlineBin(const SGPath& absoluteFileName)
         if (hash_pos != std::string::npos)
             line.resize(hash_pos);
 
+        if (line.length() == 0) continue;
+
         // and process further
         std::stringstream in(line);
 

simgear/scene/tgdb/LineFeatureBin.cxx

@@ -58,6 +58,8 @@ LineFeatureBin::LineFeatureBin(const SGPath& absoluteFileName, const std::string
         std::string line;
         std::getline(stream, line);
 
+        if (line.length() == 0) continue;
+
         // strip comments
         std::string::size_type hash_pos = line.find('#');
         if (hash_pos != std::string::npos)