get_envparam_double: do not goto into a branch

I'm not necessarily against every goto in general, but jumping into a
branch is definitely a bad idea.  Better refactor.

gc.c

@@ -9389,13 +9389,15 @@ get_envparam_double(const char *name, double *default_value, double lower_bound,
 	    }
 	}
 	else {
+            goto accept;
+	}
+    }
+    return 0;
+
   accept:
     if (RTEST(ruby_verbose)) fprintf(stderr, "%s=%f (default value: %f)\n", name, val, *default_value);
     *default_value = val;
     return 1;
-	}
-    }
-    return 0;
 }
 
 static void