[LNT] Fixed JS error caused by selecting the function with missing counters on the profile page

Some counters may be missing for some functions. These functions are labeled as `no data` on the Profile page.
You will get the JS error `value.toFixed is not a function` after selecting such function and the control flow graph.
This patch fixes this error.

OS Laboratory. Huawei Russian Research Institute. Saint-Petersburg

Reviewed By: thopre

Differential Revision: https://reviews.llvm.org/D114584

Author: Pavel Kosov

lnt/server/ui/static/lnt_profile.js

@@ -20,8 +20,8 @@ function CFGBasicBlock (instructions, fallThruInstruction, cfg) {
     this.noFallThru = gjt[0];
     this.weight = this.instructions
         .reduce(function (a,b) {
-            var weight_a = (a.weight === undefined)?a:a.weight;
-            var weight_b = (b.weight === undefined)?b:b.weight;
+            var weight_a = (a.weight === undefined)?0:a.weight;
+            var weight_b = (b.weight === undefined)?0:b.weight;
             return weight_a+weight_b;
         }, 0);
 };