Don't assert when given an empty range.

llvm::RawMemoryObject handles empty ranges just fine, and the assert can
be triggered in the wild by e.g. invoking clang with a file that
included an empty pre-compiled header file when clang has been built
with assertions enabled. Without assertions enabled, clang will properly
report that the empty file is not a valid PCH.

llvm-svn: 158769

llvm/lib/Support/StreamableMemoryObject.cpp

@@ -20,7 +20,7 @@ class RawMemoryObject : public StreamableMemoryObject {
 public:
   RawMemoryObject(const unsigned char *Start, const unsigned char *End) :
     FirstChar(Start), LastChar(End) {
-    assert(LastChar > FirstChar && "Invalid start/end range");
+    assert(LastChar >= FirstChar && "Invalid start/end range");
   }
 
   virtual uint64_t getBase() const { return 0; }