more NaN check business

core/src/processing/data/FloatDict.java

@@ -671,6 +671,9 @@ public class FloatDict {
         if (useKeys) {
           return count;  // don't worry about NaN values
 
+        } else if (count == 0) {  // skip the NaN check, it'll AIOOBE
+          return 0;
+
         } else {  // first move NaN values to the end of the list
           int right = count - 1;
           while (values[right] != values[right]) {