fix: ensure empty keys are not added to the environment

There appears to be cases where empty keys related to the basher path are injected into the env, causing identifier issues. This completely removes that possibiity.

basher.go

@@ -213,6 +213,11 @@ func (c *Context) buildEnvfile() (string, error) {
 	file.Write([]byte("export SELF=" + os.Args[0] + "\n"))
 	file.Write([]byte("export SELF_EXECUTABLE='" + c.SelfPath + "'\n"))
 	for _, kvp := range c.vars {
+		pair := strings.SplitN(kvp, "=", 2)
+		if len(pair) != 2 || strings.TrimSpace(pair[0]) == "" {
+			continue
+		}
+
 		file.Write([]byte("export " + strings.Replace(
 			strings.Replace(kvp, "'", "\\'", -1), "=", "=$'", 1) + "'\n"))
 	}