cmd/go: don't assume decimal in test_fuzz_mutate_crash

In the float test in test_fuzz_mutate_crash, don't assume the mutator
will generate a decimal during mutation. The probability it will is
quite high, but it is not guaranteed, which can cause a flake. Since we
are not really testing that the mutator will do this kind of mutation,
just that a mutation happens, just check that the input is not the zero
value like the rest of the targets.

Fixes golang#52852

Change-Id: I4640be640204ced01b4dc749c74b46da968ea7df
Reviewed-on: https://go-review.googlesource.com/c/go/+/405855
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Auto-Submit: Roland Shoemaker <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: rolandshoemaker

src/cmd/go/testdata/script/test_fuzz_mutate_crash.txt

@@ -241,8 +241,7 @@ func FuzzBool(f *testing.F) {
 
 func FuzzFloat(f *testing.F) {
 	f.Fuzz(func(t *testing.T, a float64) {
-		if a != float64(int64(a)) {
-			// It has a decimal, so it was mutated by division
+		if a != 0 {
 			panic("this input caused a crash!")
 		}
 	})