Prevent panic in Context.GetQuery() when there is no Request

[pofl]

I have an endpoint that uses an optional query parameter via DefaultQuery().
In one unit test case I want to test the route with that parameter.
I write that test as

	w := httptest.NewRecorder()
	c, _ := gin.CreateTestContext(w)
	routeHandler(c)

And this panics when routeHandler() calls c.DefaultQuery() because c.Request == nil.

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[codecov]

Codecov Report

Merging #2412 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2412   +/-   ##
=======================================
  Coverage   98.72%   98.72%           
=======================================
  Files          41       41           
  Lines        2356     2359    +3     
=======================================
+ Hits         2326     2329    +3     
  Misses         17       17           
  Partials       13       13           

Impacted Files	Coverage Δ
context.go	98.09% <100.00%> (+0.01%)	⬆️

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[pofl]

I have nothing to add to this PR anymore 😊

[thinkerou]

LGTM