[LEB128] Factor out redundant code

(cherry picked from commit 643f25f)

Author: adrian-prantl

llvm/include/llvm/Support/LEB128.h

@@ -138,17 +138,15 @@ inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr,
     if (p == end) {
       if (error)
         *error = "malformed uleb128, extends past end";
-      if (n)
-        *n = (unsigned)(p - orig_p);
-      return 0;
+      Value = 0;
+      break;
     }
     uint64_t Slice = *p & 0x7f;
     if ((Shift >= 64 && Slice != 0) || Slice << Shift >> Shift != Slice) {
       if (error)
         *error = "uleb128 too big for uint64";
-      if (n)
-        *n = (unsigned)(p - orig_p);
-      return 0;
+      Value = 0;
+      break;
     }
     Value += Slice << Shift;
     Shift += 7;