Relax this assert. It may not hold in all cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179814 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index f8f508d..f91cb54 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -1170,7 +1170,7 @@
   //   .quad except_tab1
 
   uint32_t Encoding = Frame.CompactUnwindEncoding;
-  assert(Encoding && "There should never be a null compact unwind encoding!");
+  if (!Encoding) return;
   bool DwarfEHFrameOnly = (Encoding == MOFI->getCompactUnwindDwarfEHFrameOnly());
 
   // The encoding needs to know we have an LSDA.