be a bit smarter when choosing the rebin count automatically

src/merger.cpp

@@ -86,7 +86,13 @@ results merge(const std::vector<std::string> &filenames, const std::vector<evala
 		auto &obs = entry.second;
 
 		if(rebinning_bin_count == 0) {
-			obs.rebinning_bin_count = cbrt(obs.total_sample_count);
+			// no rebinning before this
+			size_t min_bin_count = 10;
+			if(obs.total_sample_count <= min_bin_count) {
+				obs.rebinning_bin_count = obs.total_sample_count;
+			} else {
+				obs.rebinning_bin_count = min_bin_count + cbrt(obs.total_sample_count-min_bin_count);
+			}
 		} else {
 			obs.rebinning_bin_count = rebinning_bin_count;
 		}