Graceful failure saving to thumb drive... (#649)

... If renaming of the file (to a place on a different device) fails,
recover correctly before giving the warning message

src/ProjectFileIO.cpp

@@ -1903,6 +1903,12 @@ bool ProjectFileIO::SaveProject(const FilePath &fileName, const std::shared_ptr<
                OpenConnection(savedName);
             }
          }
+         else {
+            // Rename can fail -- if it's to a different device, requiring
+            // real copy of contents, which might exhaust space
+            OpenConnection(savedName);
+            return false;
+         }
       }
    }