Avoid using an invalidated iterator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148681 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Archive/ArchiveReader.cpp b/lib/Archive/ArchiveReader.cpp
index 0c89baa..a78c0f5 100644
--- a/lib/Archive/ArchiveReader.cpp
+++ b/lib/Archive/ArchiveReader.cpp
@@ -572,7 +572,11 @@
 
   SmallPtrSet<Module*, 16> Added;
   for (std::set<std::string>::iterator I=symbols.begin(),
-       E=symbols.end(); I != E; ++I) {
+         Next = I,
+         E=symbols.end(); I != E; I = Next) {
+    // Increment Next before we invalidate it.
+    ++Next;
+
     // See if this symbol exists
     Module* m = findModuleDefiningSymbol(*I,error);
     if (!m)