[turbofan] Solidify OSR deconstruction code a bit.

src/compiler/osr.cc

Index: src/compiler/osr.cc
diff --git a/src/compiler/osr.cc b/src/compiler/osr.cc
index 3ae11dac2731cfdc36a0b0000c2677a92673a5f3..6d61affe83659191a4f18060f92cd11a5eeda6b3 100644
--- a/src/compiler/osr.cc
+++ b/src/compiler/osr.cc
@@ -271,11 +271,8 @@ void OsrHelper::Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
     }
   }
 
-  if (osr_loop_entry == nullptr) {
-    // No OSR entry found, do nothing.
-    CHECK(osr_normal_entry);
-    return;
-  }
+  CHECK_NOT_NULL(osr_normal_entry);  // Should have found the OSR normal entry.
+  CHECK_NOT_NULL(osr_loop_entry);    // Should have found the OSR loop entry.
 
   for (Node* use : osr_loop_entry->uses()) {
     if (use->opcode() == IrOpcode::kLoop) {