[clang][CodeCoverage] Fix CoverageMapping for binary conditionals ops (#82141)

Fix an issue that produces a wrong coverage mapping when using binary
conditional operators as show in the example below.

Before this patch:

    1|      1|int binary_cond(int x) {
    2|      1|  x = x ?: 4;
    3|      1|  int y = 0;
    4|      0|  return x;       <-- Not covered
    5|      1|}

After this patch:

    1|      1|int binary_cond(int x) {
    2|      1|  x = x ?: 4;
    3|      1|  int y = 0;
    4|      1|  return x;       <-- Covered
    5|      1|}

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index c10d85e..d8fa69d 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1942,6 +1942,8 @@ struct CounterCoverageMappingBuilder
 
       extendRegion(E->getTrueExpr());
       OutCount = propagateCounts(TrueCount, E->getTrueExpr());
+    } else {
+      OutCount = TrueCount;
     }
 
     extendRegion(E->getFalseExpr());