pkg/proc: pad variable mem in extractVarInfoFromEntry (#3365)

* pkg/proc: pad variable mem in extractVarInfoFromEntry

On 64 bit system, the byte size of the following struct is 16:
    type myStruct struct {
       a int
       b uint32
    }
But extractVarInfoFromEntry only allocates a mem of 12 bytes for it.
When calling method of this struct with the "call" command, it will
result in this error:
    write out of bounds

This patch extends the mem by adding padding bytes to the end of the
mem.

Fixes #3364.

* move the padding logic into newCompositeMemory

pkg/proc/variables_test.go

@@ -1267,6 +1267,7 @@ func TestCallFunction(t *testing.T) {
 		{`regabistacktest("one", "two", "three", "four", "five", 4)`, []string{`:string:"onetwo"`, `:string:"twothree"`, `:string:"threefour"`, `:string:"fourfive"`, `:string:"fiveone"`, ":uint8:8"}, nil},
 		{`regabistacktest2(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)`, []string{":int:3", ":int:5", ":int:7", ":int:9", ":int:11", ":int:13", ":int:15", ":int:17", ":int:19", ":int:11"}, nil},
 		{`issue2698.String()`, []string{`:string:"1 2 3 4"`}, nil},
+		{`issue3364.String()`, []string{`:string:"1 2"`}, nil},
 		{`regabistacktest3(rast3, 5)`, []string{`:[10]string:[10]string ["onetwo","twothree","threefour","fourfive","fivesix","sixseven","sevenheight","heightnine","nineten","tenone"]`, ":uint8:15"}, nil},
 		{`floatsum(1, 2)`, []string{":float64:3"}, nil},
 	}