Fixed another fuzz-found bug

Author: cmaglie

README.md

@@ -113,10 +113,11 @@ To give you an idea on how it works, the following table shows some examples of
 | ------------------ | ------------------ |
 | `1.2.4`            | `1.2.4;`           |
 | `1.3.0-rc`         | `1.3.0-;rc`        |
-| `1.3.0-rc.0`       | `1.3.0-;rc.:0`     |
-| `1.3.0-rc.5`       | `1.3.0-;rc.:5`     |
-| `1.3.0-rc.5+build` | `1.3.0-;rc.:5`     |
-| `1.3.0-rc.20`      | `1.3.0-;rc.::20`   |
+| `1.3.0-rc.0`       | `1.3.0-;rc,:0`     |
+| `1.3.0-rc.5`       | `1.3.0-;rc,:5`     |
+| `1.3.0-rc.5+build` | `1.3.0-;rc,:5`     |
+| `1.3.0-rc.20`      | `1.3.0-;rc,::20`   |
+| `1.3.0-rc-`        | `1.3.0-;rc-`       |
 | `1.3.0`            | `1.3.0;`           |
 | `1.20.0`           | `1.:20.0;`         |
 | `1.90.0`           | `1.:90.0;`         |

testdata/fuzz/FuzzComparators/175b79ab7e360ad6

@@ -0,0 +1,3 @@
+go test fuzz v1
+string("0.0.2-rc-")
+string("0.0.2-rc.0")

version.go

@@ -480,7 +480,10 @@ func (v *Version) SortableString() string {
 	for curr, c := range prerelease {
 		if c == '.' {
 			add(prerelease[start:curr])
-			res += "."
+			// separate the pre-release pieces with a "," to ensure the correct ordering
+			// of the pre-release pieces (the separator must be lower than any other allowed
+			// character [a-zA-Z0-9-]).
+			res += ","
 			start = curr + 1
 			continue
 		}