[Fix] nvm_nvmrc_invalid_msg: respect --silent

The invalid `.nvmrc` message, which includes the file's parsed content, was printed even when `NVM_SILENT` was set (eg, by `nvm use --silent`), unlike nvm's other `.nvmrc` messages. It is now suppressed there too; the exit status still reports the invalid file.

This is hardening, not a vulnerability fix: since 67268ebc (the fix for ANT-2026-G9REVGKT), the content of a symlinked `.nvmrc` is never shown, so this message only ever shows the content of a regular `.nvmrc`.
Found by Anthropic's OSS Scanner while analyzing ANT-2026-G9REVGKT.

test/fast/Unit tests/nvm_process_nvmrc_content respects NVM_SILENT

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+: nvm.sh
+\. ../../../nvm.sh
+
+\. ../../common.sh
+
+try_err nvm_process_nvmrc_content 'secret=hunter2'
+[ "${CAPTURED_EXIT_CODE}" = '1' ] || die "expected exit code 1; got ${CAPTURED_EXIT_CODE}"
+case "${CAPTURED_STDERR}" in
+  *'invalid .nvmrc!'*'secret=hunter2'*) ;;
+  *) die "expected the invalid .nvmrc message; got >${CAPTURED_STDERR}<" ;;
+esac
+
+NVM_SILENT=1
+try_err nvm_process_nvmrc_content 'secret=hunter2'
+unset NVM_SILENT
+[ "${CAPTURED_EXIT_CODE}" = '1' ] || die "expected exit code 1 with NVM_SILENT=1; got ${CAPTURED_EXIT_CODE}"
+[ -z "${CAPTURED_STDERR}" ] || die "expected no output with NVM_SILENT=1; got >${CAPTURED_STDERR}<"