fix empty string error in Printf (#50011)

* fix empty string error in Printf

* Update runtests.jl

* Update runtests.jl

Author: aplavin

stdlib/Printf/src/Printf.jl

@@ -122,7 +122,6 @@ end
 
 # parse format string
 function Format(f::AbstractString)
-    isempty(f) && throw(InvalidFormatStringError("Format string must not be empty", f, 1, 1))
     bytes = codeunits(f)
     len = length(bytes)
     pos = 1

stdlib/Printf/test/runtests.jl

@@ -339,7 +339,6 @@ end
     @test Printf.@sprintf("1%%2%%3") == "1%2%3"
     @test Printf.@sprintf("GAP[%%]") == "GAP[%]"
     @test Printf.@sprintf("hey there") == "hey there"
-    @test_throws Printf.InvalidFormatStringError Printf.Format("")
     @test_throws Printf.InvalidFormatStringError Printf.Format("%+")
     @test_throws Printf.InvalidFormatStringError Printf.Format("%.")
     @test_throws Printf.InvalidFormatStringError Printf.Format("%.0")
@@ -488,6 +487,10 @@ end
     @test @sprintf("%d", 3//1) == "3"
     @test @sprintf("%d", Inf) == "Inf"
     @test @sprintf(" %d", NaN) == " NaN"
+
+    # 50011
+    @test Printf.@sprintf("") == ""
+    @test Printf.format(Printf.Format("")) == ""
 end
 
 @testset "integers" begin