preprocessor: stop macro-argument scan on an unexpected/EOF token

ConsumeAndParseMacroCall's `while (parameters_size > 0)` argument loop only
handled MacroArg, ',' and ')'. An unterminated macro call (e.g. `\`FOO(` at
end of file) leaves the current token as EOF, which matches none of the
three branches, so neither token_iter nor parameters_size advances and the
loop spins forever -- a hang when linting or serving a truncated/untrusted
.sv (both reach this via AnalyzeAutomaticPreprocessFallback with
expand_macros=true). Break out on any other token; the existing trailing
loop already back-fills the remaining parameters with default TokenInfo,
the same terminal state an early ')' produces.

Note: a related path (GenerateBypassWhiteSpaces dereferencing an exhausted
generator when a macro-expansion token sequence lacks a trailing EOF
sentinel) can crash on similar input; happy to follow up separately.

Signed-off-by: Eylon Krause <eylon1909@gmail.com>

verible/verilog/preprocessor/verilog-preprocess.cc

diff --git a/verible/verilog/preprocessor/verilog-preprocess.cc b/verible/verilog/preprocessor/verilog-preprocess.cc
index 2f77111..d8f5f5b 100644
--- a/verible/verilog/preprocessor/verilog-preprocess.cc
+++ b/verible/verilog/preprocessor/verilog-preprocess.cc
@@ -268,6 +268,12 @@
     if ((*token_iter)->text() == ")") {
       break;
     }
+    // Any other token -- in particular the EOF token from an unterminated
+    // macro call -- would otherwise leave token_iter and parameters_size
+    // unchanged and spin this loop forever. Stop scanning; the loop below
+    // back-fills the remaining parameters with default TokenInfo (the same
+    // terminal state produced by an early ')').
+    break;
   }
   if (parameters_size > 0) {
     while (parameters_size--) {