docs(common/models): applies PR suggestion

Co-authored-by: Marc Durdin <marc@durdin.net>

common/predictive-text/worker/model-compositor.ts

@@ -74,6 +74,17 @@ class ModelCompositor {
     if(!(transformDistribution instanceof Array)) {
       transformDistribution = [ {sample: transformDistribution, p: 1.0} ];
     } else if(transformDistribution.length == 0) {
+      /*
+         Robust stop-gap: if our other filters somehow fail, this fixes the 
+         zero-length array by making it match the form of the array that
+         would result if it were instead called with the other legal 
+         parameter type - a single Transform.
+
+         Unfortunately, the method will lack all data about even 
+         the original keystroke that resulted in the call... but this way, 
+         we can at least get some predictions rather than shortcutting 
+         and producing none whatsoever.      
+      */
       transformDistribution.push({
         sample: {
           insert: '',