Internals: Fix assertion if bad display

src/V3EmitCFunc.cpp

@@ -247,14 +247,14 @@ void EmitCFunc::displayArg(AstNode* dispp, AstNode** elistp, bool isScan, const
     AstNode* argp = nullptr;
     if (!ignore) {
         argp = *elistp;
-        // Prep for next parameter
-        *elistp = (*elistp)->nextp();
         if (VL_UNCOVERABLE(!argp)) {
             // expectDisplay() checks this first, so internal error if found here
             dispp->v3error(
                 "Internal: Missing arguments for $display-like format");  // LCOV_EXCL_LINE
             return;  // LCOV_EXCL_LINE
         }
+        // Prep for next parameter
+        *elistp = (*elistp)->nextp();
         if (argp->widthMin() > VL_VALUE_STRING_MAX_WIDTH) {
             dispp->v3warn(E_UNSUPPORTED, "Unsupported: Exceeded limit of "
                                              + cvtToStr(VL_VALUE_STRING_MAX_WIDTH)