Fix possible segfault in page checksum error message.

The STRDEF definition of plural is out of scope in the error message just below it, which may lead to either garbage in the log message or a crash with SIGSEGV.

This is particularly visible with pg_tde, which encrypts tables: if pgbackrest is run with checksum enabled, it tries to emit this message for all encrypted files.

Fix by using simple char * constants in the error message.

doc/xml/release/2025/2.57.0.xml

@@ -1,5 +1,18 @@
 <release date="XXXX-XX-XX" version="2.57.0dev" title="Under Development">
     <release-core-list>
+        <release-bug-list>
+            <release-item>
+                <github-pull-request id="2675"/>
+
+                <release-item-contributor-list>
+                    <release-item-contributor id="zsolt.parragi"/>
+                    <release-item-reviewer id="david.steele"/>
+                </release-item-contributor-list>
+
+                <p>Fix possible segfault in page checksum error message.</p>
+            </release-item>
+        </release-bug-list>
+
         <release-improvement-list>
             <release-item>
                 <github-pull-request id="2661"/>

doc/xml/release/contributor.xml

@@ -1225,3 +1225,8 @@
     <contributor-name-display>yummyliu</contributor-name-display>
     <contributor-id type="github">yummyliu</contributor-id>
 </contributor>
+
+<contributor id="zsolt.parragi">
+    <contributor-name-display>Zsolt Parragi</contributor-name-display>
+    <contributor-id type="github">dutow</contributor-id>
+</contributor>

src/command/backup/backup.c

@@ -1568,12 +1568,12 @@ backupJobResult(
                                 }
 
                                 // Make message plural when appropriate
-                                const String *const plural = errorTotalMin > 1 ? STRDEF("s") : EMPTY_STR;
+                                const char *const plural = errorTotalMin > 1 ? "s" : "";
 
                                 // ??? Update formatting after migration
                                 LOG_WARN_FMT(
-                                    "invalid page checksum%s found in file %s at page%s %s", strZ(plural), strZ(fileLog),
-                                    strZ(plural), strZ(error));
+                                    "invalid page checksum%s found in file %s at page%s %s", plural, strZ(fileLog), plural,
+                                    strZ(error));
                             }
                         }
                     }