[BOLT] Zero initialize pre-aggregated counters (#142698)

#140196 introduced UB by using uninitialized misprediction count for
pre-aggregated traces. Fix by zero initializing both counters.

Test Plan: updated entry-point-fallthru.s

Author: aaupov

bolt/lib/Profile/DataAggregator.cpp

@@ -1220,7 +1220,7 @@ std::error_code DataAggregator::parseAggregatedLBREntry() {
   // Storage for parsed fields.
   StringRef EventName;
   std::optional<Location> Addr[3];
-  int64_t Counters[2];
+  int64_t Counters[2] = {0};
 
   while (Type == INVALID || Type == EVENT_NAME) {
     while (checkAndConsumeFS()) {

bolt/test/X86/entry-point-fallthru.s

@@ -6,6 +6,10 @@
 # RUN: link_fdata %s %t %t.preagg PREAGG
 # RUN: perf2bolt %t -p %t.preagg --pa -o %t.fdata | FileCheck %s
 # CHECK: traces mismatching disassembled function contents: 0
+# RUN: FileCheck %s --check-prefix=CHECK-FDATA --input-file %t.fdata
+# CHECK-FDATA:      1 main 0 1 main 6 0 1
+# CHECK-FDATA-NEXT: 1 main e 1 main 11 0 1
+# CHECK-FDATA-NEXT: 1 main 11 1 main 0 0 1
 
 	.globl main
 main: