linux/configure.ac: Fix tesseract conditional problem. (#1504)

Fixes #1503.

Using tesseract-ocr's stock pkg-config, it would produce an error due to
unquoted whitespace:

  $ test ! -z `pkg-config --libs-only-l --silence-errors tesseract`
  bash: test: syntax error: `-larchive' unexpected

* linux/configure.ac: Use a positive test, and double-quote the $() command
substitution.

Co-authored-by: Carlos Fernandez Sanz <[email protected]>

Author: apteryks

docs/CHANGES.TXT

@@ -11,6 +11,7 @@
 - Fix: missing `#` in color attribute of font tag
 - Fix: ffmpeg 5.0, tesseract 5.0 compatibility and remove deprecated methods
 - Fix: tesseract 5.x traineddata location in ocr
+- Fix: fix autoconf tesseract detection problem (#1503)
 - Fix: add missing compile_info_real.h source to Autotools build
 
 0.94 (2021-12-14)

linux/configure.ac

@@ -149,7 +149,7 @@ AS_IF([ (test x$ocr = xtrue || test x$hardsubx = xtrue) && test ! $HAS_LEPT -gt
 AM_CONDITIONAL(HARDSUBX_IS_ENABLED, [ test x$hardsubx = xtrue ])
 AM_CONDITIONAL(OCR_IS_ENABLED, [ test x$ocr = xtrue || test x$hardsubx = xtrue ])
 AM_CONDITIONAL(FFMPEG_IS_ENABLED, [ test x$ffmpeg = xtrue ])
-AM_CONDITIONAL(TESSERACT_PRESENT, [ test ! -z  `pkg-config --libs-only-l --silence-errors tesseract` ])
+AM_CONDITIONAL(TESSERACT_PRESENT, [ test -n  "$(pkg-config --libs-only-l --silence-errors tesseract)" ])
 AM_CONDITIONAL(TESSERACT_PRESENT_RPI, [ test -d "/usr/include/tesseract" && test `ls -A /usr/include/tesseract | wc -l` -gt 0 ])
 AM_CONDITIONAL(SYS_IS_LINUX, [ test `uname -s` = "Linux"])
 AM_CONDITIONAL(SYS_IS_MAC, [ test `uname -s` = "Darwin"])