Fix gemini round 2 findings: explicit length guard on ROCm version file parser

Both _detect_rocm_version (install_python_stack.py) and
_detect_host_rocm_version (install_llama_prebuilt.py) read /opt/rocm/.info/version
or $ROCM_PATH/lib/rocm_version, split on "." and unconditionally accessed
parts[1]. The surrounding broad `except Exception: pass` already swallowed
the resulting IndexError, so a one-component file like "6\n" did fall
through to the next detection source -- but the control flow relied on
exception handling instead of an explicit check.

Add `if len(parts) >= 2:` guards in both helpers so the loop falls through
on its own without raising. Behaviour is unchanged for the common multi-
component case; the previously-silent IndexError path becomes an explicit
no-op.

studio/install_llama_prebuilt.py

@@ -3007,7 +3007,11 @@ def _detect_host_rocm_version() -> tuple[int, int] | None:
         try:
             with open(path) as fh:
                 parts = fh.read().strip().split("-")[0].split(".")
-            return int(parts[0]), int(parts[1])
+            # Explicit length guard avoids relying on the broad except
+            # below to swallow IndexError when the version file contains
+            # a single component (e.g. "6\n" on a partial install).
+            if len(parts) >= 2:
+                return int(parts[0]), int(parts[1])
         except Exception:
             pass
     amd_smi = shutil.which("amd-smi")

studio/install_python_stack.py

@@ -55,7 +55,11 @@ def _detect_rocm_version() -> tuple[int, int] | None:
         try:
             with open(path) as fh:
                 parts = fh.read().strip().split("-")[0].split(".")
-            return int(parts[0]), int(parts[1])
+            # Explicit length guard avoids relying on the broad except
+            # below to swallow IndexError when the version file contains
+            # a single component (e.g. "6\n" on a partial install).
+            if len(parts) >= 2:
+                return int(parts[0]), int(parts[1])
         except Exception:
             pass