#990 lb reader- update code per PR

- Small changes for clarity.

src/vt/vrt/collection/balance/read_lb.cc

@@ -64,16 +64,16 @@ namespace vt { namespace vrt { namespace collection { namespace balance {
 /*static*/ bool ReadLBSpec::read_complete_ = false;
 
 /*static*/ bool ReadLBSpec::openSpec(std::string const& filename) {
-  // Ignore attempt to open same spec.
-  if (not open_filename_.empty() and open_filename_ == filename) {
-    return true;
-  }
-
   // No-op if no file specified. Can't be used to clear.
   if (filename.empty()) {
     return false;
   }
 
+  // Ignore attempt to open same spec.
+  if (not open_filename_.empty() and open_filename_ == filename) {
+    return true;
+  }
+
   vtAssert(
     open_filename_.empty(),
     "Spec already opened. Use clear first to load again."
@@ -332,7 +332,7 @@ auto excluded_str = [](SpecIndex idx) -> std::string {
   std::stringstream ss;
 
   if (open_filename_.empty()) {
-    return "";
+    return "[No LB Spec open]";
   }
 
   if (not ReadLBSpec::getExactEntries().empty()) {

src/vt/vrt/collection/balance/read_lb.h

@@ -182,10 +182,16 @@ struct ReadLBSpec {
   using ParamMapType = std::map<std::string, std::string>;
 
   /**
-   * \brief Prepare the spec for reading, if it exists.
+   * \brief Opens and reads the spec file, if it exists.
    *
-   * This will also ensure the spec is loaded.
-   * This method MUST be called before the other methods.
+   * This method MUST be called before the other access methods.
+   *
+   * \param[in] filename The path to the file to read.
+   *
+   * \pre A different spec file is not currently open.
+   * \pre The filename refers to a valid spec file.
+   *
+   * \return True if the spec was opened and can be used.
    */
   static bool openSpec(std::string const& filename);