pcre2test: avoid printing invalid utf trail in partial match

When match_invalid_utf is enabled, invalid UTF-8 data can't match
but it was mistakenly getting printed as part of a partial match
eventhough the ovector correctly didn't include it, as shown by:

  PCRE2 version 10.34 2019-11-21
    re> /(?<=..)X/match_invalid_utf,allvector
  data> XX\x80\=ph,ovector=1
  Partial match: \x{80}
  ** ovector[1] is not equal to the subject length: 2 != 3
   0: 2 2

Fix the logic to print instead the empty match that was returned
and as a side effect avoid a buffer overread when trying to decode
UTF-8 that was missing code units.

Fixes: PCRE2Project#235

Author: carenas

.gitignore

@@ -66,6 +66,10 @@ testtemp2
 testtemp2grep
 testtry
 testtrygrep
+testSinput
+testbtables
+testsaved1
+testsaved2
 
 m4/libtool.m4
 m4/ltoptions.m4

src/pcre2test.c

@@ -8064,7 +8064,7 @@ for (gmatched = 0;; gmatched++)
     rubriclength += 15;
 
     PCHARS(backlength, pp, leftchar, ovector[0] - leftchar, utf, outfile);
-    PCHARSV(pp, ovector[0], ulen - ovector[0], utf, outfile);
+    PCHARSV(pp, ovector[0], ovector[1] - ovector[0], utf, outfile);
 
     if ((pat_patctl.control & CTL_JITVERIFY) != 0 && jit_was_used)
       fprintf(outfile, " (JIT)");

testdata/testinput10

@@ -506,6 +506,10 @@
 \= Expect no match
     ab\x80cdef\=ph
 
+/(?<=..)X/match_invalid_utf
+    XX\x80\=ph
+    XX\xef\=ph
+
 /ab$/match_invalid_utf
     ab\x80cdeab
 \= Expect no match

testdata/testoutput10

@@ -1646,6 +1646,14 @@ Partial match: ab
     ab\x80cdef\=ph
 No match
 
+/(?<=..)X/match_invalid_utf
+    XX\x80\=ph
+Partial match: 
+** ovector[1] is not equal to the subject length: 2 != 3
+    XX\xef\=ph
+Partial match: 
+** ovector[1] is not equal to the subject length: 2 != 3
+
 /ab$/match_invalid_utf
     ab\x80cdeab
  0: ab