flo_to_s: 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.

numeric.c

@@ -985,6 +985,10 @@ flo_to_s(VALUE flt)
 	memcpy(ptr -= decpt, buf, digs);
     }
     else {
+        goto exp;
+    }
+    return s;
+
   exp:
     if (digs > 1) {
         memmove(buf + 2, buf + 1, digs - 1);
@@ -996,7 +1000,6 @@ flo_to_s(VALUE flt)
     buf[1] = '.';
     rb_str_cat(s, buf, digs + 1);
     rb_str_catf(s, "e%+03d", decpt - 1);
-    }
     return s;
 }