ffStrbufLastIndexC: account for empty strings

#285

src/detection/terminalshell/terminalshell_linux.c

@@ -224,7 +224,6 @@ static void getShellVersionZsh(FFstrbuf* exe, FFstrbuf* version)
         "--version",
         NULL
     });
-    ffStrbufTrimRight(version, '\n');
     ffStrbufSubstrBeforeLastC(version, ' ');
     ffStrbufSubstrAfterFirstC(version, ' ');
 }

src/util/FFstrbuf.h

@@ -184,6 +184,9 @@ static inline FF_C_NODISCARD uint32_t ffStrbufFirstIndexS(const FFstrbuf* strbuf
 
 static inline FF_C_NODISCARD uint32_t ffStrbufLastIndexC(const FFstrbuf* strbuf, char c)
 {
+    if(strbuf->length == 0)
+        return strbuf->length;
+
     return ffStrbufPreviousIndexC(strbuf, strbuf->length - 1, c);
 }