[Object] fixed invalid symbol handling in ELFObjectFile::getSymbolName

Found a bug in ElfObjectFile.h that occurred when there was an invalid Symbol Name in an object file. This error affected the behavior of the Expected<> value and leading it to abort, rather than behave as normal. I found this as I was adding tests to llvm-cm, as prompted by @jhenderson.

Without this fix, upon encountering an invalid symbol and trying tot l get its name, the program states that
```Expected<T> must be checked before access or destruction```
 and aborts.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D154665

Author: JestrTulip

llvm/include/llvm/Object/ELFObjectFile.h

@@ -530,10 +530,10 @@ Expected<StringRef> ELFObjectFile<ELFT>::getSymbolName(DataRefImpl Sym) const {
 
   // If the symbol name is empty use the section name.
   if ((*SymOrErr)->getType() == ELF::STT_SECTION) {
-    if (Expected<section_iterator> SecOrErr = getSymbolSection(Sym)) {
-      consumeError(Name.takeError());
+    Expected<section_iterator> SecOrErr = getSymbolSection(Sym);
+    if (SecOrErr)
       return (*SecOrErr)->getName();
-    }
+    return SecOrErr.takeError();
   }
   return Name;
 }

llvm/test/tools/llvm-objdump/ELF/section-symbols.test

@@ -19,6 +19,11 @@
 # CHECK-NEXT: 00000003 R_X86_64_NONE            {{$}}
 # CHECK-NEXT: 00000004 R_X86_64_NONE            {{$}}
 
+## Test that we consume an error in ELFObjectFile<ELFT>::getSectionName when disassembling. 
+# RUN: llvm-objdump -d --syms %t1 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t1 --check-prefix=CHECK-DISAS
+# CHECK-DISAS: warning: '[[FILE]]': invalid section index: 67
+
 --- !ELF
 FileHeader:
   Class:   ELFCLASS32