[sanitizer] Add workaround for empty strings

[vitalybuka]

Summary

I see crashes on this check when some reports are being generated.

[eugenis]

lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc

245

Similarly to the next block,
if (last_colon && IsDigit(last_colon[1]))

[vitalybuka]

simplified code

[vitalybuka]

comment

[eugenis]

lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc

249

handle the empty line case

[vitalybuka]

handle empty strings

[eugenis]

LGTM

lib/sanitizer_common/sanitizer_symbolizer_libcdep.cc

 
 // Parse a <file>:<line>[:<column>] buffer. The file path may contain colons on
 // Windows, so extract tokens from the right hand side first. The column info is
 // also optional.
 static const char *ParseFileLineInfo(AddressInfo *info, const char *str) {
   char *file_line_info = 0;
   str = ExtractToken(str, "\n", &file_line_info);
   CHECK(file_line_info);
-  // Parse the last :<int>, which must be there.
-  char *last_colon = internal_strrchr(file_line_info, ':');
-  CHECK(last_colon);
-  int line_or_column = internal_atoll(last_colon + 1);
-  // Truncate the string at the last colon and find the next-to-last colon.
-  *last_colon = '\0';
-  last_colon = internal_strrchr(file_line_info, ':');
-  if (last_colon && IsDigit(last_colon[1])) {
-    // If the second-to-last colon is followed by a digit, it must be the line
-    // number, and the previous parsed number was a column.
-    info->line = internal_atoll(last_colon + 1);
-    info->column = line_or_column;
-    *last_colon = '\0';
-  } else {
-    // Otherwise, we have line info but no column info.
-    info->line = line_or_column;
-    info->column = 0;
+
+  info->line = 0;
+
+  char* back = file_line_info + internal_strlen(file_line_info) - 1;
+  for (int i = 0; i < 2; ++i) {
+    while (back > file_line_info && IsDigit(*back))
+      --back;
+    if (*back != ':' || !IsDigit(back[1]))
+      break;
+    info->column = info->line;
+    info->line = internal_atoll(back + 1);
+    *back = '\0';
+    --back;
   }
+
   ExtractToken(file_line_info, "", &info->file);
   InternalFree(file_line_info);
   return str;
 }
 
 // Parses one or more two-line strings in the following format:
 //   <function_name>
 //   <file_name>:<line_number>[:<column_number>]