fix bug when error is infinite (#46436)

Author: oscardssmith

base/math.jl

@@ -1176,8 +1176,8 @@ end
         xnlo += err
         n >>>= 1
     end
-    !isfinite(x) && return x*y
-    return muladd(x, y, muladd(y, xnlo, x*ynlo))
+    err = muladd(y, xnlo, x*ynlo)
+    return ifelse(isfinite(x) & isfinite(err), muladd(x, y, err), x*y)
 end
 
 function ^(x::Float32, n::Integer)

test/math.jl

@@ -1362,6 +1362,7 @@ end
     end
     # test for large negative exponent where error compensation matters
     @test 0.9999999955206014^-1.0e8 == 1.565084574870928
+    @test 3e18^20 == Inf
 end
 
 # Test that sqrt behaves correctly and doesn't exhibit fp80 double rounding.