Fix Rust generation for versions without minor or patch parts (OpenAPITools#19946)

This fixes generation of a Rust library for OpenAPI specifications
where `info.version` was a single-digit number. This happened to for
[this](https://github.com/motis-project/motis/blob/db005f2e55812b8231e2e2dbac4d3abf711a8610/openapi.yaml#L10)
specification. The fix for this issue is similar to the one in !17440.

Author: Schmiddiii

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

@@ -422,9 +422,12 @@ public void execute(Template.Fragment fragment, Writer writer) throws IOExceptio
                 content = content.trim().replace("v", "");
                 content = content.replace("V", "");
 
-                // convert 5.2 to 5.2.0 for example
                 String[] contents = content.split("[.]");
-                if (contents.length == 2) {
+                if (contents.length == 1) {
+                    // convert 5 to 5.0.0 for example
+                    content += ".0.0";
+                } else if (contents.length == 2) {
+                    // convert 5.2 to 5.2.0 for example
                     content += ".0";
                 }