Fix empty detection bug (#135)

Closes: #134

Fixes regression in post-processing from #129.

Signed-off-by: Justin Georgi <justin.georgi@gmail.com>

Reviewed-on: #135

src/pages/detection-mixin.js

@@ -43,6 +43,8 @@ export default {
         rawBoxes.push(boxCalc)
         rawScores.push(getScores)
       }
+
+      if (rawBoxes.length > 0) {
         const tBoxes = tf.tensor2d(rawBoxes)
         let tScores = null
         let structureScores = null
@@ -62,6 +64,8 @@ export default {
           }
         }
 
+        tf.dispose(tBoxes)
+        tf.dispose(tScores)
         const valid_detections_data = classes_data.length
         var output = {
           detections: []
@@ -77,14 +81,12 @@ export default {
             "confidence": scores_data[i] * 100
           })
         }
-
+      }
       tf.dispose(res)
-      tf.dispose(tBoxes)
-      tf.dispose(tScores)
       tf.dispose(input)
       console.timeEnd('post-process')
 
-      return output
+      return output || { detections: [] }
     },
     getRemoteLabels() {
       var self = this