fix: handle empty array return value in dht.findProvs (ipfs#1003)

Correcting the array check to happen before the individual element checks. fixes ipfs-inactive/js-ipfs-http-client#928

Author: KrishnaPG

src/dht/findprovs.js

@@ -23,17 +23,17 @@ module.exports = (send) => {
     }
 
     const handleResult = (res, callback) => {
+      // Inconsistent return values in the browser vs node
+      if (Array.isArray(res)) {
+        res = res[0]
+      }
+      
       // callback with an empty array if no providers are found
       if (!res) {
         const responses = []
         return callback(null, responses)
       }
 
-      // Inconsistent return values in the browser vs node
-      if (Array.isArray(res)) {
-        res = res[0]
-      }
-
       // Type 4 keys
       if (res.Type !== 4) {
         const errMsg = `key was not found (type 4)`